Audio apparatus, audio system, image display apparatus, and image projection apparatus

ABSTRACT

An audio apparatus includes a housing, a piezoelectric vibration unit provided to the housing and having a piezoelectric element, and a communication unit for receiving an audio signal. When a received audio signal is applied to the piezoelectric element while a load of the audio apparatus is applied to the piezoelectric vibration unit, the piezoelectric element is deformed causing deformation of the piezoelectric vibration unit, whereby a contact surface in contact with the audio apparatus vibrates and generate a sound.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a division of U.S. patent application Ser.No. 14/909,464 filed on Feb. 2, 2016, which is a National Phase ofInternational Application Number PCT/JP2014/004269, filed Aug. 20, 2014,and claims priority to and the benefit of Japanese Patent ApplicationsNo. 2013-174703, No. 2013-174737, and No. 2013-174838 those filed onAug. 26, 2013. The disclosures of all the above-listed prior-filedapplications are hereby in incorporated by reference herein in theirentirely.

TECHNICAL FIELD

This disclosure relates to an audio apparatus, an audio system, an imagedisplay apparatus, and an image projection apparatus.

BACKGROUND

There have conventionally been proposed various audio apparatuses thatallow a voice conference by connecting to a conference room at a remotelocation via a communication network (for example, see PLT 1). Such anaudio apparatus is provided with a microphone and a speaker and, whenbeing placed on a table or the like in a conference room, picks up asound in the room with the microphone and transmits the sound as atransmission audio signal to another audio apparatus (the other party'saudio apparatus) in the other party's conference room, as well asoutputting, from the speaker, a received audio signal (a sound in theother party's conference room) transmitted from the other party's audioapparatus. As the speaker, a dynamic speaker is typically used.

Also, for example, a conventional television receiver (hereinafter,simply referred to as a “TV”) generates a sound from a speaker providedto the TV. As the speaker of the conventional TV, the dynamic speaker istypically used and, for example, PLT 2 describes a TV using the dynamicspeaker.

Further, for example, a conventional projection apparatus generates asound from a speaker provided thereto. As the speaker of theconventional projection apparatus, the dynamic speaker is typicallyused. For example, PLT 3 describes a vibration generation apparatushaving a structure of the dynamic speaker provided with a magnet, avoice coil, a diaphragm, and a casing for accommodating thesecomponents. Frequency characteristics of the sound generated from thedynamic speaker is affected by a size of the dynamic speaker. Forexample, in order to reproduce a low-pitched sound, a large dynamicspeaker is required.

CITATION LIST Patent Literatures

PLT 1: JP-A-2008-245250

PLT 2: JP-A-2011-35552

PLT 3: JP-UM-A-5-85192

SUMMARY Technical Problem

However, since the dynamic speaker has poor sound diffusibility,depending on a positional relation with the speaker, it is difficult tohear the sound from the speaker, e.g., a volume of the sound becomessmaller in proportion to a distance from the speaker.

Also, since the dynamic speaker needs various members including themagnet, the voice coil, the diaphragm and the like, it is inevitablethat the speaker includes a large number of components. Therefore, alarge speaker leads to an increase in size of an apparatus and thus isdifficult to handle. Especially, since the TVs of a recent trend havethin designs, it is difficult to mount a large speaker thereto. As aresult, the TV and the projection apparatus are likely to have aninsufficient sound pressure in a low frequency range. Such inconvenienceis caused by the TV and the projection apparatus as well as variousimage display apparatuses and various image projection apparatuses thosemay generate a sound while displaying a still image or a video image.

Therefore, it could be helpful to provide an audio apparatus and anaudio system those capable of acquiring sounds having a small volumedifference over a wide range.

Further, it could be helpful to provide an image display apparatus andan image projection apparatus those capable of generating the sound in apreferable manner.

Solution to Problem

In order to achieve the above object, an audio apparatus disclosedherein includes:

a housing;

a piezoelectric vibration unit having a piezoelectric element providedto the housing; and

a communication unit configured to receive an audio signal, wherein

when a received audio signal is applied to the piezoelectric elementwhile a load of the audio apparatus is applied to the piezoelectricvibration unit, the piezoelectric element is deformed causingdeformation of the piezoelectric vibration unit, whereby a contactsurface in contact with the audio apparatus is vibrated generating asound.

Preferably, the piezoelectric vibration unit is arranged at a portion ofthe housing opposite to the contact surface.

The audio apparatus may include a microphone configured to pick up asound and outputting the audio signal, and the communication unit maytransmit the audio signal output from the microphone.

Preferably, the microphone is retained in the housing via a damperconfigured to reduce a vibration caused by the deformation of thepiezoelectric vibration unit.

Preferably, a vibration direction of the piezoelectric element and avibration direction of the microphone intersect with each other.

The microphone may be arranged separately from the housing.

The communication unit may receive the audio signal from another audioapparatus.

The audio apparatus may further include a speaker that is provided tothe housing and amplifies the received audio signal;

a detection unit configured to detect a contact state between thecontact surface and the piezoelectric vibration unit; and

a controller configured to control the speaker and the piezoelectricvibration unit based on the contact state detected by the detectionunit.

The piezoelectric element may be a laminated piezoelectric element anddeformed extending and contracting along a lamination direction.

The piezoelectric vibration unit may include a cover member configuredto deliver the vibration caused by the deformation of the piezoelectricelement to the contact surface and thereby vibrating the contactsurface.

The contact surface may be a placing surface having the audio apparatusplaced thereon.

In order to achieve the above object, further, an audio system disclosedherein including a microphone unit and a speaker unit, wherein

the microphone unit is provided with a microphone configured to pick upa sound and outputting an audio signal and a transmission unitconfigured to transmit the audio signal to the speaker unit,

the speaker unit is provided with a housing, a piezoelectric vibrationunit having a piezoelectric element provided to the housing, and areception unit configure to receive the audio signal, and

when the audio signal is applied to the piezoelectric element while aload of the audio apparatus is applied to the piezoelectric vibrationunit, the piezoelectric element is deformed causing deformation of thepiezoelectric vibration unit, whereby a contact surface in contact withthe audio apparatus is vibrated generating a sound.

In order to achieve the above object, an image display apparatusdisclosed herein includes:

a housing;

a display unit that is retained in the housing and displays an image;and

a controller configured to control the piezoelectric element, wherein

when the controller applies a sound signal to the piezoelectric elementwhile a load of the image display apparatus is applied to thepiezoelectric vibration unit, the piezoelectric element is deformedcausing deformation of the piezoelectric vibration unit, whereby acontact surface in contact with the image display apparatus is vibratedgenerating a sound.

The piezoelectric vibration unit may be arranged at a portion of thehousing opposite to the contact surface.

The image display apparatus may include a support member configured tosupport the housing, and the piezoelectric vibration unit may bearranged at a portion of the support member opposite to the contactsurface.

The image display apparatus may include a detection unit configured todetect a contact state between the contact surface and the piezoelectricvibration unit, and the controller may control the piezoelectric elementbased on the contact state.

The image display apparatus may include a speaker, and the controllermay drive the speaker and the piezoelectric element at the same time.

The image display apparatus may include a storage unit configured tostore frequency characteristics of the speaker, and the controller maycontrol the piezoelectric element based on the frequency characteristicsof the speaker stored.

The controller may control a sound signal to be applied to thepiezoelectric element in a manner compensating for the lack of a soundpressure of the frequency characteristics of the speaker stored.

The image display apparatus may include a recording unit configured torecord frequency characteristics of a sound generated from the contactsurface, and the controller may control the speaker based on thefrequency characteristics recorded.

The controller may control the sound pressure of the frequencycharacteristics of the speaker in a manner compensating for the lack ofthe sound pressure of the frequency characteristics recorded.

The piezoelectric element may be a laminated piezoelectric element anddeformed extending and contracting along a lamination direction.

The piezoelectric vibration unit may include a cover member configuredto deliver the vibration caused by the deformation of the piezoelectricelement to the contact surface and thereby vibrating the contactsurface.

The contact surface may be a placing surface having the image displayapparatus placed thereon.

The contact surface may be a wall surface having the image displayapparatus hung thereon.

In order to achieve the above object, an image projection apparatusdisclosed herein includes:

a housing;

a piezoelectric vibration unit having a piezoelectric element;

a projection unit retained in the housing configured to display an imageon a projection screen; and

a controller configured to control the piezoelectric element, wherein

when the controller applies a sound signal to the piezoelectric elementwhile a load of the image projection apparatus is applied to thepiezoelectric vibration unit, the piezoelectric element is deformedcausing deformation of the piezoelectric vibration unit, whereby acontact surface in contact with the image projection apparatus isvibrated and generates a sound.

The piezoelectric vibration unit may be provided at a position within apredetermined distance from a center of gravity of the image projectionapparatus and opposite to the contact surface.

The image projection apparatus may include a support member configuredto support the housing, and the piezoelectric vibration unit may beprovided at a portion of the support member opposite to the contactsurface.

The image projection apparatus may include a front support portionpositioned on a front side from the center of gravity of the imageprojection apparatus where the projection screen is located and a rearsupport portion positioned on a rear side opposite to the front sidehaving the projection screen, wherein

the piezoelectric vibration unit may be arranged at the rear supportportion.

The image projection apparatus may include a detection unit configuredto detect a contact state between the contact surface and thepiezoelectric vibration unit, and the controller controls thepiezoelectric element based on the contact state.

The image projection apparatus may include a speaker, and the controllermay drive the speaker and the piezoelectric element at the same time.

The image projection apparatus may include a storage unit configured tostore frequency characteristics of the speaker, and the controller maycontrol the piezoelectric element based on the frequency characteristicsof the speaker stored.

The controller may control a sound signal to be applied to thepiezoelectric element in a manner compensating for the lack of the soundpressure of the frequency characteristics of the speaker stored.

The image projection apparatus may include a recording unit configuredto record frequency characteristics of a sound generated from thecontact surface, and the controller may control the speaker based on thefrequency characteristics recorded.

The controller may control the sound pressure of the frequencycharacteristics of the speaker in a manner compensating for the lack ofthe sound pressure of the frequency characteristics recorded.

The piezoelectric element may be a laminated piezoelectric element anddeformed extending and contracting along a lamination direction.

The piezoelectric vibration unit may include a cover member configuredto deliver the vibration caused by the deformation of the piezoelectricelement to the contact surface and thereby vibrating the contactsurface.

The contact surface may be a placing surface having the image projectionapparatus placed thereon.

The contact surface may be a wall surface having the image projectionapparatus hung thereon.

Advantageous Effect

According to the disclosure herein, an audio apparatus and an audioapparatus those capable of acquiring sounds having a small volumedifference over a wide range may be provided.

According to the disclosure herein, further, an image display apparatusand an image projection apparatus those capable of generating the soundin an excellent manner may be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1A is an external perspective view of an audio apparatus accordingto a first embodiment;

FIG. 1B is a side view of the audio apparatus of FIG. 1A;

FIG. 2 is an explanatory view of a piezoelectric vibration unit and aholder portion therefor;

FIG. 3A is an enlarged cross-sectional view illustrating a structure ofa laminated piezoelectric element;

FIG. 3B is a plan view of the laminated piezoelectric element of FIG.3A;

FIG. 4 is a diagram illustrating an example of variations of thelaminated piezoelectric element;

FIG. 5 is a partially enlarged cross-sectional view of the piezoelectricvibration unit;

FIG. 6 is a functional block diagram of a section of the audioapparatus;

FIG. 7 is a functional block diagram illustrating an example of aconfiguration of a piezoelectric element drive unit;

FIG. 8 is a diagram illustrating an example of frequency characteristicsof an LPF;

FIG. 9 is a diagram illustrating an example of arrangements of thepiezoelectric vibration unit and legs;

FIG. 10A is an explanatory diagram of a sound generating operationcarried out by the audio apparatus;

FIG. 10B is an explanatory diagram of the sound generating operationcarried out by the audio apparatus;

FIG. 10C is an explanatory diagram of the sound generating operationcarried out by the audio apparatus;

FIG. 11 is a diagram illustrating another example of the arrangements ofthe piezoelectric vibration unit and the legs;

FIG. 12 is a diagram illustrating an example of a configuration of avoice conference system including the audio apparatus of FIG. 1;

FIG. 13 is a perspective view illustrating a schematic configuration ofan audio apparatus according to a second embodiment;

FIG. 14 is a perspective view illustrating a schematic configuration ofan audio apparatus according to a third embodiment;

FIG. 15 is a perspective view illustrating an example of variations ofthe third embodiment;

FIG. 16 is a perspective view illustrating a schematic configuration ofan audio apparatus according to a fourth embodiment;

FIG. 17 is a functional block diagram of a section of the audioapparatus of FIG. 16;

FIG. 18 is a flowchart illustrating an example of an operation of theaudio apparatus of FIG. 16;

FIG. 19 is a perspective view illustrating a schematic configuration ofan audio system according to a fifth embodiment;

FIG. 20 is a functional block diagram of a section of the audio systemof FIG. 19;

FIG. 21A is an elevation view illustrating a schematic configuration ofan image display apparatus according to a sixth embodiment;

FIG. 21B is a side view of the image display apparatus of FIG. 21A;

FIG. 22 is a schematic perspective view of a section illustrated in anexploded view of a front side of a housing of FIG. 21A;

FIG. 23 is a partially enlarged cross-sectional view of a piezoelectricvibration unit of FIG. 21A;

FIG. 24 is a functional block diagram of a section of a TV of FIG. 21A;

FIG. 25 is a flowchart illustrating an operation of a controller of FIG.24;

FIG. 26A is an explanatory view of an example of sound signal controlaccording to a sixth embodiment;

FIG. 26B is an explanatory view of another example of the sound signalcontrol according to the sixth embodiment;

FIG. 27 is a diagram illustrating arrangements of a piezoelectricvibration unit and a support in a TV of FIG. 21A;

FIG. 28A is a schematic diagram explaining an operation of thepiezoelectric vibration unit in the TV of FIG. 21A;

FIG. 28B is a schematic diagram explaining the operation of thepiezoelectric vibration unit in the TV of FIG. 21A;

FIG. 28C is a schematic diagram explaining the operation of thepiezoelectric vibration unit in the TV of FIG. 21A;

FIG. 29A is an elevation view illustrating a schematic configuration ofan image display apparatus according to a seventh embodiment;

FIG. 29B is a side view of the image display apparatus of FIG. 29A;

FIG. 30 is a side view illustrating a schematic configuration of animage display apparatus according to an eighth embodiment;

FIG. 31 is a side view of the image display apparatus according to theeighth embodiment when assuming that there is no wall surface;

FIG. 32A is an external perspective view illustrating a schematicconfiguration of an image projection apparatus according to a ninthembodiment;

FIG. 32B is an elevation view of the image projection apparatus of FIG.32A;

FIG. 32C is a side view of the image projection apparatus of FIG. 32A;

FIG. 33 is a schematic perspective view of a section illustrated in anexploded view of a bottom side of the image projection apparatus of FIG.32A;

FIG. 34 is a partially enlarged cross-sectional view of a piezoelectricvibration unit of FIG. 32B;

FIG. 35 is a functional block diagram of a section of the imageprojection apparatus of FIG. 32A;

FIG. 36 is a flowchart illustrating an operation of a controller of FIG.35;

FIG. 37A is an explanatory view of an example of sound signal controlaccording to a ninth embodiment;

FIG. 37B is an explanatory view of another example of the sound signalcontrol according to the ninth embodiment;

FIG. 38 is a diagram illustrating an arrangement of a piezoelectricvibration unit in the image projection apparatus of FIG. 32A;

FIG. 39A is a schematic diagram explaining an operation of thepiezoelectric vibration unit in the image projection apparatus of FIG.38;

FIG. 39B is a schematic diagram explaining the operation of thepiezoelectric vibration unit in the image projection apparatus of FIG.38;

FIG. 39C is a schematic diagram explaining the operation of thepiezoelectric vibration unit in the image projection apparatus of FIG.38;

FIG. 40A is an external perspective view illustrating an imageprojection apparatus according to a tenth embodiment;

FIG. 40B is an elevation view of the image projection apparatus of FIG.40A;

FIG. 40C is a side view of the image projection apparatus of FIG. 40A;

FIG. 41 is a diagram illustrating a comparison of the blurring of aprojected image of the image projection apparatus according to the tenthembodiment;

FIG. 42 is a side view illustrating a schematic configuration of animage projection apparatus according to an eleventh embodiment;

FIG. 43A is a diagram illustrating an example of variations of a holdingmanner of the piezoelectric vibration unit;

FIG. 43B is a diagram illustrating another example of the variations ofthe holding manner of the piezoelectric vibration unit;

FIG. 43C is a diagram illustrating yet another example of the variationsof the holding manner of the piezoelectric vibration unit; and

FIG. 44 is a diagram illustrating a schematic configuration of a sectionillustrating an example of variations of the piezoelectric vibrationunit.

DETAILED DESCRIPTION

Hereinafter, embodiments of the disclosure will be described withreference to the accompanying drawings.

First Embodiment

FIGS. 1A and 1B are a perspective view and a side view, respectively,those illustrating a schematic configuration of an audio apparatusaccording to a first embodiment. An audio apparatus 10 according to thepresent embodiment includes a housing 20 in a shape allowing placementthereof on a table 200 set in a conference room. Although the housing 20in FIGS. 1A and 1B takes a substantially disc-shape as an external shapethereof, the housing 20 may take any shape as long as allowing placementthereof on the table 200. The table 200 is an example of a contactsurface in contact with the audio apparatus 10. In the followingdescription, the table 200 is referred to as a contact surface 200 or aplacement surface 200. The housing 20 includes an upper surface 20 ahaving an operation unit 30 and a microphone 40 arranged thereon and abottom surface 20 b having legs 50 and a piezoelectric vibration unit 60arranged thereon.

The operation unit 30 includes a known display unit 32 such as a liquidcrystal display for displaying an operation key 31 such as a dial keyand a function key for inputting a telephone number and the like of theother party of telephone conference, as well as for displayinginformation input with the operation key 31. The microphone 40 picks upa voice of a conference participant and the like therearound and outputsa transmission audio signal. The microphone 40 may be constituted byusing a known microphone such as a capacitor microphone or a dynamicmicrophone. According to the present embodiment, the microphone 40 isretained by the housing 20 via, for example, a damper 70 made of rubberor the like. The legs 50 are made of an elastic material such as, forexample, rubber, silicone, polyurethane and the like and provided to thebottom surface 20 b in a manner supporting, together with thepiezoelectric vibration unit 60, the housing 20 on the table 200.

FIG. 2 is an explanatory view of the piezoelectric vibration unit 60 anda holder portion therefor. The piezoelectric vibration unit 60, asillustrated in a partial cross-section of a bottom portion of thehousing 20 in FIG. 2, is accommodated and held in a holder portion 100formed in the housing 20. The piezoelectric vibration unit 60 isdisposed at a position opposed to the contact surface 200 of the housing20. The holder portion 100 has a slit 101 with a uniform width openingto the bottom surface 20 b of the housing 20 and extending in adirection perpendicular to the bottom surface 20 b when the housing 20is placed on a horizontal surface.

The piezoelectric vibration unit 60, as illustrated in an explodeddiagram in FIG. 2, includes a piezoelectric element 61, an O-ring 62,and a cap 63 that serves as an insulating cover member. Thepiezoelectric element 61 is an element that, upon application of anelectric signal (voltage) thereto, extends and contracts, or bends, inaccordance with an electromechanical coupling coefficient of aconstituent material. The piezoelectric element 61 is made of, forexample, ceramic or crystal. The piezoelectric element 61 may be aunimorph, a bimorph, or a laminated piezoelectric element. The laminatedpiezoelectric element includes a laminated bimorph element formed withlaminated bimorphs (for example, 8 to 40 layers thereof) and a laminatedpiezoelectric element of a stack type having a lamination structureformed with a plurality of dielectric layers made of, for example, PZT(lead zirconate titanate) and electrode layers disposed therebetween.The unimorph extends and contracts upon application of the electricsignal thereto, and the bimorph bents upon application of the electricsignal thereto. The laminated piezoelectric element of the stack typeextends and contracts along a lamination direction upon application ofthe electric signal thereto.

According to the present embodiment, the piezoelectric element 61 is thelaminated piezoelectric element of the stack type. The laminatedpiezoelectric element 61, as illustrated in an enlarged cross-sectionalview in FIG. 3A and a plan view in FIG. 3B, for example, is formed byalternately laminating dielectrics 61 a made of ceramics such as PZT andinternal electrodes 61 b with a comb-shaped cross-section. The internalelectrode 61 b electrically connected to a first side electrode 61 c andthe internal electrode 61 b electrically connected to a second sideelectrode 61 d are alternately laminated.

The laminated piezoelectric element 61 illustrated in FIGS. 3A and 3Bincludes one end portion having a first lead connection portion 61 eelectrically connected to the first side electrode 61 c and a secondlead connection portion 61 f electrically connected to the second sideelectrode 61 d formed thereon. To the first lead connection portion 61 eand the second lead connection portion 61 f, a first lead line 61 g anda second lead line 61 h are connected, respectively. Also, the firstside electrode 61 c, the second side electrode 61 d, the first leadconnection portions 61 e, and the second lead connection portions 61 fare covered with an insulating layer 61 i in a state in which the firstlead connection portion 61 e and the second lead connection portion 61 fare connected to the first lead line 61 g and the second lead line 61 h,respectively.

The laminated piezoelectric element 61 has a length of, for example, 5mm to 120 mm in a lamination direction. A cross-sectional shape of thelaminated piezoelectric element 61 orthogonal to the laminationdirection may be a substantially square shape of 2 mm by 2 mm to 10 mmto 10 mm, or any shape other than the square shape. The number of layersand size of the cross-sectional area of the laminated piezoelectricelement 61 are appropriately determined based on weight of the audioapparatus 10 in a manner sufficiently ensuring a sound pressure or soundquality of a sound generated from the contact surface such as the tablein contact with the piezoelectric vibration unit 60.

To the laminated piezoelectric element 61, as described later, areceived audio signal is supplied from the controller via apiezoelectric element drive unit. In other words, a voltagecorresponding to the audio signal is applied to the laminatedpiezoelectric element 61 by the controller via the piezoelectric elementdrive unit. In the case that an AC voltage is applied as the voltage bythe controller, when a positive voltage is applied to the first sideelectrode 61 c, a negative voltage is applied to the second sideelectrode 61 d, and, on the other hand, when the negative voltage isapplied to the first side electrode 61 c, the positive voltage isapplied to the second side electrode 61 d. When the voltages are appliedto the first side electrode 61 c and the second side electrode 61 d,polarization occurs in the dielectric 61 a, causing extension andcontraction of the laminated piezoelectric element 61 from a statethereof with no voltage applied thereto. The laminated piezoelectricelement 61 extends and contracts in a direction substantially along alamination direction of the dielectric 61 a and the internal electrode61 b. Or, the laminated piezoelectric element 61 extends and contractsin a direction substantially coincides with the lamination direction ofthe dielectric 61 a and the internal electrode 61 b. Since the laminatedpiezoelectric element 61 extends and contracts substantially along thelamination direction thereof, there is an advantage of offeringexcellent vibration transmission efficiency in the extending andcontracting direction.

We have conceived that the laminated piezoelectric element 61 mayeffectively serve as a vibration element for generating a received voicefrom the contact surface 200 of the table or the like in contact withthe audio apparatus 10.

In FIGS. 3A and 3B, the first side electrode 61 c and the second sideelectrode 61 d may have a through-hole connection alternately connectedto the internal electrode 61 b and also connected to the first leadconnecting portion 61 e and the second lead connecting portion 61 f,respectively. Or, the first lead connecting portion 61 e and the secondlead connecting portion 61 f of FIGS. 3A and 3B may be formed on thefirst side electrode 61 c and the second side electrode 61 d,respectively, at one end of the laminated piezoelectric element 61 asillustrated in FIG. 4.

The laminated piezoelectric element 61, as illustrated in a partiallyenlarged cross-sectional view in FIG. 5, includes one lateral endportion having the first lead connecting portion 61 e and the secondlead connecting portion 61 f those fixed to the slit 101 of the holderportion 100 of the housing 20 via adhesive 102 (for example, epoxyresin). Also, the other end portion of the laminated piezoelectricelement 61 is capped with a cap 63 and fixed by the adhesive 102.

The cap 63 is made of a material such as, for example, hard plastic orthe like that may reliably deliver extending and contracting vibrationof the laminated piezoelectric element 61 to the placing surface (thecontact surface) such as the table. If it is desired to suppressdamaging the placing surface, the cap 63 may be made of relatively softplastic rather than the hard plastic. The cap 63 includes an entryportion 63 a and a protrusion portion 63 b. When the cap 63 is attachedto the laminated piezoelectric element 61, the entry portion 63 a islocated inside the slit 101, and the protrusion portion 63 b protrudesfrom the housing 20. An O-ring 62 is provided to a circumference of theentry portion 63 a located inside the slit 101. The O-ring 62 is madeof, for example, silicone rubber. The O-ring 62 movably supports thelaminated piezoelectric element 61 and, simultaneously, preventsmoisture and dust from entering the slit 101. The protrusion portion 63b is formed in a hemispherical shape at one end thereof. The end of theprotrusion portion 63 b is not limited to take the hemispherical shapebut may take any shape as long as reliably point-contacting orsurface-contacting the placing surface (the contact surface) of thetable or the like and capable of delivering the extending andcontracting vibration of the laminated piezoelectric element 61. Whenthe piezoelectric vibration unit 60 is attached to the holder portion100, the protrusion portion 63 b of the cap 63 protrudes from the bottomsurface 20 b of the housing 20. The protrusion portion 63 b of the cap63 has a facing surface 63 c opposite to the bottom 20 b of the housing20. As illustrated in FIG. 5, when the laminated piezoelectric element61 has no voltage applied thereto and thus is not extending andcontracting, the facing surface 63 c is spaced apart from the bottomsurface 20 b by a distance d.

FIG. 6 is a functional block diagram of a section of the audio apparatus10 according to the present embodiment. The audio apparatus 10 includes,in addition to the operation key 31, the display unit 32, the microphone40, and the laminated piezoelectric element 61 those described above, acommunication unit 110, a piezoelectric element drive unit 120, and acontroller 130. The operation key 31, the display unit 32, themicrophone 40, and the communication unit 110 are connected to thecontroller 130. The laminated piezoelectric element 61 is connected tothe controller 130 via the piezoelectric element drive unit 120.

The communication unit 110 is connected, via a telephone line or acommunication cable such as an Ethernet (registered trademark) cable, orin a wireless manner, to a communication network such as a publictelephone line or IP network. The controller 130 is a processor forcontrolling the entire operation of the audio apparatus 10. Thecontroller 130 applies the audio signal (for example, a voltagecorresponding to the audio signal of the other party of the call)received by the communication unit 110 to the laminated piezoelectricelement 61 via the piezoelectric element drive unit 120.

The piezoelectric element drive unit 120, as illustrated in FIG. 7 byway of example, includes a signal processor circuit 121, a boostercircuit 122, and a low-pass filter (LPF) 123. The signal processorcircuit 121 is constituted by using, for example, a digital signalprocessor (DSP) or the like having an equalizer and an A/D conversioncircuit. The signal processor circuit 121 carries out necessary signalprocessing such as equalization processing and D/A conversion processingon a digital signal received from the controller 130 and thus generatesan analogue audio signal and outputs the analogue audio signal to thebooster circuit 122. The function of the signal processor circuit 121may be incorporated in the controller 130.

The booster circuit 122 boosts the voltage of the analog audio signalthat has been input and applies thus obtained signal to the laminatedpiezoelectric element 61 via the LPF 123. A maximum voltage of the audiosignal applied to the laminated piezoelectric element 61 by the boostercircuit 122 may be, for example, in a range of 10 Vpp to 50 Vpp but notlimited thereto. The maximum voltage may be appropriately adjusted basedon the weight of the audio apparatus 10 and performance of the laminatedpiezoelectric element 61. The audio signal applied to the laminatedpiezoelectric element 61 may have a biased DC voltage having the maximumvoltage set therearound.

Not only the laminated piezoelectric element 61 but the piezoelectricelements generally have more power loss in proportion to a frequency.Therefore, the LPF 123 is set to have frequency characteristics toattenuate or cut at least a portion of a frequency component atapproximately 10 kHz to 50 kHz or higher, or frequency characteristicsto increase an attenuation rate gradually or in stages. FIG. 8illustrates the frequency characteristics of the LPF 123 having acut-off frequency at approximately 20 kHz by way of example Attenuationor cutting the high frequency component in this manner allowssuppressing power consumption as well as heat generation by thelaminated piezoelectric element 61.

Next, an example of arrangements of the piezoelectric vibration unit 60and the legs 50 will be described. FIG. 9 illustrates a state in whichthe audio apparatus 10 is placed with the bottom surface 20 b facingdown on the placing surface 200 of the table or the like that ishorizontal. The table is an example of a contact object of the audioapparatus 10, and the placing surface 200 is an example of the contactsurface (placing surface) in contact with the audio apparatus 10. In theexample of the arrangements illustrated in FIG. 9, the piezoelectricvibration unit 60 is disposed on the periphery of the bottom surface 20b and, together with a plurality of legs 50 arranged on the periphery ofthe bottom surface 20 b in a similar manner, supports the audioapparatus 10 on the placing surface 200 at multiple positions (forexample, four positions). A dot G represents a center of gravity of theaudio apparatus 10.

In FIG. 9, the leg 50 includes a lowermost end portion 501, which is aportion in contact with the placing surface 200 when the audio apparatus10 is placed with the bottom surface 20 b facing down on the placingsurface 200 of the table or the like that is horizontal.

The piezoelectric vibration unit 60 includes a lowermost portion 601,which is a portion in contact with the placing surface 200 when theaudio apparatus 10 is placed with the bottom surface 20 b facing down onthe placing surface 200 of the table or the like that is horizontal. Thelowermost end portion 501 is, for example, a tip of the cap 63.

The audio apparatus 10 includes a lowermost end portion 101. Thelowermost end portion 101 of the audio apparatus 10 is a portion incontact with the placing surface 200 when the audio apparatus 10 isplaced with the bottom surface 20 b facing down on the placing surface200 of the table or the like that is horizontal, assuming that there isno piezoelectric vibration unit 60. The lowermost end portion 101 of theaudio apparatus 10 is, for example, an edge of the housing 20 but notlimited thereto. When the bottom surface 20 b has a protrusion portionprotruding therefrom, the protrusion portion may serve as the lowermostend portion 101 of the audio apparatus 10.

In FIG. 9, a dotted line L represents a line (a virtual line) passingthrough the center of gravity G of the audio apparatus 10 andperpendicular to the placing surface 200 when the audio apparatus 10 isplaced with the bottom surface 20 b facing down on the placing surface200 of the table or the like that is horizontal. A dashed line Irepresents a line (a virtual line) passing through the lowermost endportion 101 in contact with the placing surface 200 and the line L andparallel to the placing surface 200, assuming that there is nopiezoelectric vibrating unit 60.

In FIG. 9, a region R1 is one of regions of the audio apparatus 10separated by the line L, and a region R2 is the other. The legs 50 areprovided on the bottom surface 20 in the region RE The piezoelectricvibration unit 60 is provided on the bottom surface 20 b in the regionR2.

In this case, the piezoelectric vibration unit 60 is preferablypositioned as close to the line L as possible on the bottom surface 20 bin the region R2. Thereby, a load applied to the piezoelectric vibrationunit 60 becomes larger than that when the piezoelectric vibration unit60 is positioned remote from the line L on the bottom surface 20 b inthe region R2.

The legs 50 are preferably positioned as remote from the line L aspossible on the bottom surface 20 b in the region RE Thereby, when thepiezoelectric vibration unit 60 is positioned as close to the line L aspossible, a sufficient distance is ensured between the legs 50 and thepiezoelectric vibration unit 60, allowing stable placement of the audioapparatus 10 on the placing surface 200.

A lowermost portion 601 of the piezoelectric vibration unit 60, at thetime of maximum extension of the laminated piezoelectric element 61 froma non-extending/contracting state thereof having no voltage appliedthereto, or at the time of maximum amplitude of the laminatedpiezoelectric element 61, may position between the dotted line I and theplacing surface 200. That is, the lowermost portion 601, at the time ofmaximum extension of the laminated piezoelectric element 61 from thenon-extending/contracting state thereof with no voltage applied thereto,or at the time of maximum amplitude of the laminated piezoelectricelement 61, may protrude from the dotted line I toward the placingsurface 200. Thereby, the piezoelectric vibration unit 60 mayappropriately vibrate the placing surface 200.

Also, the lowermost portion 601 of the piezoelectric vibration unit 60,at the time of maximum contraction of the laminated piezoelectricelement 61 from the non-extending/contracting state thereof with novoltage applied thereto, or at the time of minimum amplitude of thelaminated piezoelectric element 61, may position between the dotted lineI and the placing surface 200. That is, the lowermost portion 601, atthe time of maximum contraction of the laminated piezoelectric element61 from the non-extending/contracting state thereof with no voltageapplied thereto, or at the time of minimum amplitude of the laminatedpiezoelectric element 61, may protrude from the dotted line I toward theplacing surface 200. Thereby, the lowermost portion 101 of the audioapparatus 10 becomes less likely to contact the placing surface 200 and,for example, depending on a type of coating of the housing 20, thecoating becomes less likely to come off. Also, an abnormal noise is lesslikely to be generated between the lowermost portion 101 and the placingsurface 200.

FIGS. 10A, 10B, and 10C are explanatory diagrams of a sound generatingoperation of the audio apparatus 10 according to the present embodiment.The audio apparatus 10, as illustrated in FIG. 10A, is placed in such amanner that the bottom surface 20 b of the housing 20 faces down and thecap 63 of the piezoelectric vibration unit 60 and the legs 50 contactthe placing surface (contact surface) 200 of the table or the like.Thereby, the weight of the audio apparatus 10 is applied as a load tothe piezoelectric vibration unit 60. In a state illustrated in FIG. 10A,the laminated piezoelectric element 61 has no voltage applied theretoand thus is not extending and contracting.

In this a state, when the laminated piezoelectric element 61 of thepiezoelectric vibration unit 60 is driven upon the audio signal, thelaminated piezoelectric element 61, as illustrated in FIGS. 10B and 10C,by using a portion (or portions) of any one or a plurality of legs 50 incontact with the placing surface (the contact surface) 200 as a support(supports), vibrates extending (FIG. 10B) and contracting (FIG. 10C)according to the audio signal, during which the cap 63 stays in contactwith the placing surface (the contact surface) 200. Specifically, FIG.10B shows a state when the piezoelectric vibration unit 60 is deformedin response to the audio signal and extends or projects (in comparisonwith FIG. 10A) outwardly from the housing 20, as indicated by the arrowin FIG. 10B. FIG. 10C shows another state when the piezoelectricvibration unit 60 is deformed in response to the audio signal andretracts or contracts (in comparison with FIG. 10A) inwardly into thehousing 20, as indicated by the arrow in FIG. 10C. As far as notinducing a disadvantage such as generation of the abnormal noise causedby the lowermost portion 101 contacting the placing surface 200, the cap63 may be slightly spaced apart from the placing surface (the contactsurface) 200. A difference between a length of the laminatedpiezoelectric element 61 at the time of maximum extension and a lengththereof at the time of maximum contraction is, for example, 0.05 μm to50 μm. Thereby, the extending and contracting vibration of the laminatedpiezoelectric element 61 is delivered to the placing surface 200 via thecap 63, and the placing surface 200 vibrates and, serving as a vibrationspeaker, generates a sound. When the difference between the length ofthe laminated piezoelectric element 61 at the time of maximum extensionand the length thereof at the time of maximum contraction is smallerthan 0.05 μm, the placing surface 200 may possibly not be vibratedappropriately. On the other hand, when the difference is greater than 50μm, the placing surface 200 vibrates too much, possibly rattling theaudio apparatus 10.

As described above, the tip of the cap 63, at the time of maximumextension of the laminated piezoelectric element 61, may positionbetween the dotted line I and the placing surface 200 in FIG. 9. Also,the tip of the cap 63, at the time of maximum contraction of thelaminated piezoelectric element 61, may position between the dotted lineI and the placing surface 200.

Also, the distance d between the bottom surface 20 b and the facingsurface 63 c of the cap 63 may be longer than a displacement amount ofthe laminated piezoelectric element from the non-extending/contractingstate thereof with no voltage applied thereto to the maximum contractionstate. Thereby, when the laminated piezoelectric element 61 contractsmaximum (a state illustrated in FIG. 10C), the bottom surface 20 b ofthe housing 20 and the cap 63 becomes less likely to come into contactwith each other. As a result, the cap 63 becomes less likely to come offthe piezoelectric element 61.

A position of the piezoelectric element 60 on the bottom surface 20 b, alength of the laminated piezoelectric element 61 in the laminationdirection, a size of the cap 63 and the like are appropriatelydetermined in a manner satisfying the above conditions.

Next, with reference to FIG. 11, another example of the arrangements ofthe piezoelectric vibration unit 60 and the legs 50 will be described.In the another example of the arrangements illustrated in FIG. 11, aplurality of (3 or more) legs 50 are disposed at the periphery of thebottom surface 20 b of the housing 20 and, in a central portion of thebottom surface 20 b, the piezoelectric vibration unit 60 is positionedon a vertical line passing through the center of gravity G when theaudio apparatus 20 is placed on a horizontal surface. Accordingly, whenfour legs 50 are provided, the audio apparatus 10 is supported by fourlegs 50 and one piezoelectric element 60 on the placing surface 200.

In FIG. 11, the line L, similarly to that in FIG. 9, is a line (avirtual line) passing through the center of gravity G of the audioapparatus 10 and perpendicular to the placing surface 200 when the audioapparatus 10 is placed with the bottom surface 20 b facing down on theplacing surface 200 of the table or the like that is horizontal. In FIG.11, pairs of legs 50 are provided across the dotted line L that passesthrough the center of gravity G of the audio apparatus 10. In this case,the number of the legs 50 is an even number of at least 4. A dotted lineL1 is a line (a virtual line) passing through the legs 50 on one sideand perpendicular to the placing surface 200. A dotted line L2 is a line(a virtual line) passing through the legs 50 on the other side andperpendicular to the placing surface 200. The dotted line L1 is spacedapart from the line L by a distance D1 in a horizontal direction. Thedotted line L2 is spaced apart from the line L by a distance D2 in thehorizontal direction.

In FIG. 11, a region R1 is one of regions separated by the dotted lineL, and the region R2 is the other. The legs 50 on one side, on thebottom surface 20 b, are arranged in the region R1 being spaced apartfrom the piezoelectric vibration unit 60 by a distance D1 in thehorizontal direction. The legs 50 on the other side, on the bottomsurface 20 b, are arranged in the region R2 being spaced apart from thepiezoelectric vibration unit 60 by a distance D2 in the horizontaldirection.

The piezoelectric vibration unit 60 is provided on the dotted line L onthe bottom surface 20 b. That is, the piezoelectric vibration unit 60 isdisposed on a line passing through the center of gravity G of the audioapparatus 10 and perpendicular to the placing surface 200 when the audioapparatus 10 is placed with the bottom surface 20 b facing down on theplacing surface 200 that is horizontal. Thereby, the weight of the audioapparatus 10 may be applied as the load to the piezoelectric vibrationunit 60, and the extending and contracting vibration of thepiezoelectric vibration unit 60 may be efficiently delivered to theplacing surface (the contact surface) 200. When D1=D2 is satisfied, thatis, when a pair of legs 50 are disposed in a symmetrical manner withrespect to the piezoelectric vibration unit 60, the audio apparatus 10may be stably placed on the placing surface 200.

The piezoelectric vibration unit 60, when the laminated piezoelectricelement 61 is driven upon the audio signal, vibrates extending andcontracting according to the audio signal, during which the cap 63 staysin contact with the placing surface (the contact surface) 200. As far asnot inducing the disadvantage such as generation of the abnormal noisecaused by the lowermost portions of the legs 51 contacting the placingsurface 200, the lowermost portions of the legs 50 may be slightlyspaced apart from the placing surface (the contact surface) 200 when thepiezoelectric vibration unit 60 is driven.

The legs 50, when the audio apparatus 10 is placed with the bottomsurface 20 b facing down on the placing surface 200 of the table that ishorizontal, receives the weight of the audio apparatus 10 as the loadand thus is elastically deformed. That is, the legs 50, due to theweight of the audio apparatus 10, contracts in a direction perpendicularto the placing surface 200. In a state in which the laminatedpiezoelectric element 61 has no voltage applied thereto and thus is notextending and contracting, an elastic deformation amount of the legs 50is preferably greater than the displacement amount of the laminatedpiezoelectric element 61 from no-extending/contracting state thereofwith no voltage applied thereto to the maximum extension state. Thereby,at the time of maximum extension of the laminated piezoelectric element61, the legs 50 are less likely to separate from the placing surface200, allowing the stable placement of the audio apparatus 10 on theplacing surface 200.

FIG. 12 is a diagram illustrating an example of a configuration of avoice conferencing system (an audio system) having the audio apparatus10 according to the present embodiment. The audio apparatus 10 isconnected to the audio apparatus 10 of the other party at a remotelocation via communication network NW such as the public telephone lineor the IP network. Each of the audio apparatuses 10 is connected to thecommunication network NW via the communication cable such as thetelephone line or the Ethernet (registered trademark) cable, or in thewireless manner. An audio signal transmitted from the audio apparatus 10on this side is sent to the audio apparatus 10 of the other party of theconference, and an audio signal from the audio apparatus 10 of the otherparty of the conference is output from the contact surface such as thetable having the audio apparatus 10 on this side placed thereon. In thismanner, the audio conferencing is performed. It is a matter of coursethat the other party of the conference may use an audio apparatus with aconventional structure.

Since the audio apparatus 10 according to the present embodiment usesthe piezoelectric element as a vibration source, the audio apparatus 10may be smaller and lighter than a conventional audio apparatus having adynamic speaker. Also, since the audio apparatus 10 outputs a sound byvibrating the contact surface of the table or the like having the audioapparatus 10 placed thereon, regardless of a distance from the audioapparatus and without directivity, a sound may be output at homogeneousvolume, providing homogeneous and excellent audio characteristics over awide area in the conference room. Therefore, unlike the conventionalaudio apparatus having the dynamic speaker, there is no need to increasethe sound around the audio apparatus. Moreover, since the microphone 40is retained in the housing 20 via the damper 70, the vibration of thepiezoelectric vibration unit 60 delivered to the microphone 40 may beefficiently attenuated. Therefore, a sneak sound to the microphone 40may be reduced, whereby noise such as echo may be also reduced.

Also, since the laminated piezoelectric element 61 of the stuck type isused as the piezoelectric element and caused to vibrate extending andcontracting along the lamination direction upon the audio signal and,also, the extending and contracting vibration is delivered to theplacing surface (the contact surface) 200, the vibration in an extendingand contracting direction may be efficiently delivered to the placingsurface (the contact surface) 200, efficiently vibrating the placingsurface (the contact surface) 200. Further, since the laminatedpiezoelectric element 61 is in contact with the placing surface (thecontact surface) 200 via the cap 63, the laminated piezoelectric element61 may be prevented from being damaged. Also, since the weight of theaudio apparatus 10 is applied as the load to the cap 63, the cap 63 mayreliably contact the placing surface (contact surface) 200 andefficiently deliver the extending and contracting vibration of thepiezoelectric vibration unit 60 to the placing surface (contact surface)200.

Second Embodiment

FIG. 13 is a perspective view illustrating a schematic structure of anaudio apparatus according to a second embodiment. An audio apparatus 11according to the present embodiment is composed of the audio apparatus10 according to the first embodiment, to which a plurality ofmicrophones 40 are provided (facing each of four directions of two linesorthogonal to each other in FIG. 13). The microphone 40 is arranged on alateral side 20 c of the housing 20 in such a manner that a vibrationdirection (indicated by a bidirectional arrow A) of a diaphragmconstituting the microphone 40 intersects with, or preferably becomesorthogonal to, a vibration direction of the piezoelectric vibration unit60 (indicated by a bidirectional arrow B). The microphones 40 may beattached to the housing 20 directly or via the damper similarly to thefirst embodiment. The other structures are similar to the firstembodiment, and the same components are provided with the same referencenumerals and descriptions thereof will be omitted.

According to the present embodiment, since a vibration direction A ofthe diaphragm of the microphone 40 intersects with a vibration directionB of the piezoelectric vibration unit 60, the vibration of thepiezoelectric vibration unit 60 delivered to the microphone 40 may bemore efficiently attenuated. Therefore, the sneak sound to themicrophone 40 may be reduced, whereby noise such as echo may be alsoreduced. Such an effect is exhibited especially significantly when themicrophone 40 is retained in the housing 20 via the damper.

Third Embodiment

FIG. 14 is a perspective view illustrating a schematic structure of anaudio apparatus according to a third embodiment. An audio apparatus 12according to the present embodiment is composed of the audio apparatus11 according to the second embodiment having each of the plurality ofmicrophones 40 separated from the housing 20 serving as a body. Theother structures are similar to the second embodiment, and the samecomponents are provided with the same reference numerals anddescriptions thereof will be omitted. The microphones 40, via cables 41or in the wireless manner, are connected to a controller 130 arranged inthe housing 20 (see FIG. 6). The microphones 40 may be used being placedon the contact surface of the table or the like having the housing 20placed thereon, or being worn by conference participants in a manner ofpin microphones.

Separation of the microphones 40 from the body in this manner allows themicrophones 40 to be located close to the conference participants.Therefore, without enhancing microphone sensitivity, a transmissionvoice may be efficiently converted into the electric signal.Accordingly, the sneak sound of the output received voice to themicrophone 40 may be reduced, whereby noise such as echo may be alsoreduced. When the microphone 40 is used being placed on the contactsurface of the table or the like having the housing 20 placed thereon,as illustrated in FIG. 15, each of the microphones 40 are preferablyprovided with a plurality of legs 42 made of an elastic material similarto the legs 50 of the housing 20. Thereby, the legs 42 may attenuate thevibration of the contact surface delivered to the microphone 40,reducing the sneak sound to the microphone 40 and thus reducing thenoise such as the echo.

Fourth Embodiment

FIG. 16 is a perspective view illustrating a schematic structure of anaudio apparatus according to a fourth embodiment. An audio apparatus 13according to the present embodiment is composed of the audio apparatus11 according to the second embodiment further including a speaker 80 anda detection unit 90. The other structures are similar to the secondembodiment, and the same components are provided with the same referencenumerals and descriptions thereof will be omitted. The speaker 80 is asound output device for outputting the audio signal and constituted byusing, for example, a small dynamic speaker having excellent frequencycharacteristics in a high sound area, a piezoelectric speaker, acapacitance speaker, or the like. The speaker 80 is disposed in thehousing 20 in a manner outputting the received voice from the uppersurface 20 a of the housing 20.

The detection unit 90 is disposed on the bottom surface 20 b of thehousing 20 and detects whether the piezoelectric vibration unit 60 is incontact with the placing surface 200, that is, detects a contact statebetween the placing surface (the contact surface) 200 and thepiezoelectric vibration unit 60. The detection unit 90 is constituted byusing a device capable of detecting the contact state between theplacing surface 200 and the piezoelectric vibration unit 60 such as, forexample, an infrared sensor, an ultrasonic sensor, a proximity sensor, amechanical switch, a camera, a pressure sensor, or the like. Thedetection unit 90 may be constituted by using the piezoelectricvibration unit 60 by using an output thereof as the sensor. The speaker80 and the detection unit 90, as illustrated in a functional blockdiagram in FIG. 17, are connected to the controller 130.

FIG. 18 is a flowchart illustrating an example of an operation of theaudio apparatus 13 according to the present embodiment. First, thecontroller 130 checks whether there is the audio signal (step S101).When there is no audio signal (No), the controller 130 ends this flowwithout applying the audio signals to the laminated piezoelectricelement 61 and the speaker 80. When there is the audio signal (Yes), thecontroller 130 outputs the audio signal to the speaker 80 (step S102).

Next, the controller 130 checks whether the detection unit 90 isdetecting the contact between the piezoelectric vibration unit 60 andthe placing surface 200 (step S103). When the detection unit 90 is notdetecting the contact between the piezoelectric vibration unit 60 andthe placing surface 200 (No), the controller 130 does not output theaudio signal to the laminated piezoelectric element 61. In this case,the received voice is not generated from the placing surface 200 butoutput from the speaker 80 alone.

On the other hand, when the detection unit 90 is detecting the contactbetween the piezoelectric vibration unit 60 and the placing surface 200(Yes), the controller 130 outputs the audio signal to the laminatedpiezoelectric element 61 via the piezoelectric element drive unit 120(see FIG. 6) (step S104). In this case, the received voice is generatedfrom both the speaker 80 and the placing surface 200. The controller130, by repeating the series of operations in FIG. 18, based on thecontact state between the piezoelectric vibration unit 60 and theplacing surface 200, controls the output of the audio signals to thespeaker 80 and the piezoelectric element 61.

As described above, when the piezoelectric vibration unit 60 is incontact with the placing surface 200 and the audio signal is output fromboth the placing surface 200 and the speaker 80, since the speaker 80has excellent frequency characteristics in the high sound area and theplacing surface 200 has excellent frequency characteristics in arelatively low sound area, a sound with excellent frequencycharacteristics overall across the low sound area to the high sound areamay be output. Also, the speaker 80 having the excellent frequencycharacteristics in the high sound area can be small in size, allowing areduction in size and weight of the entire audio apparatus.

Although according to the present embodiment, when the piezoelectricvibration unit 60 is in contact with the placing surface 200, the audiosignals are output from both the placing surface 200 and the speaker 80,the audio signal may be output from the placing surface 200 alone. Also,when the audio signals are output from both the placing surface 200 andthe speaker 80, the sound output from the placing surface 200 isdetected and the frequency characteristics of the audio signal to beapplied to the speaker 80 may be controlled in a manner compensating forthe lack of frequency characteristics of the output sound. Or, thefrequency characteristics of the sound signal to be applied to thelaminated piezoelectric element 61 may be corrected in a mannercompensating for the lack of the frequency characteristics of thespeaker 80.

Fifth Embodiment

FIG. 19 is a perspective view illustrating a schematic configuration ofan audio system according to a fifth embodiment. The audio systemaccording to the present embodiment includes a microphone unit 45 and anaudio apparatus 14 separate from each other. The audio apparatus 14constitutes a speaker unit and includes the housing 20 and thepiezoelectric vibration unit 60 retained in the housing 20. Thepiezoelectric vibration unit 60 has the configuration similar to that inthe above embodiments and retained by the housing 20 in a similarmanner.

FIG. 20 is a block diagram of a section of the audio system according tothe present embodiment. The microphone unit 45 includes a microphone 46for picking up the sound and outputting the audio signal and atransmission unit 47 for wirelessly transmitting the audio signal fromthe microphone 46. The audio apparatus 14 includes a reception unit 150for receiving the audio signal wirelessly transmitted from thetransmission unit 47 of the microphone unit 45, the piezoelectricelement drive unit 120 for driving the laminated piezoelectric element61 constituting the piezoelectric vibration unit 60, and the controller130.

In the audio system according to the present embodiment, the microphoneunit 45 picks up the sound by using the microphone 46 and wirelesslytransmits the audio signal from the transmission unit 47. The audiosignal transmitted from the microphone unit 45 is received by thereception unit 150 of the audio apparatus 14, input to the controller130, and then applied to the laminated piezoelectric element 61 by thecontroller 130 via the piezoelectric element drive unit 120. Thereby,the contact surface having the audio apparatus 14 placed thereon and incontact with the piezoelectric vibration unit 60 vibrates generating areproduced sound.

According to the present embodiment, similarly to the above embodiments,the audio apparatus 14 may generate sounds having a small volumedifference over a wide range via the surface of the audio apparatus 14in contact with the contact surface. Also, since the audio signal iswirelessly transmitted from the microphone unit 45 to the audioapparatus 14, the microphone unit 45, within a range receivable of theaudio signal from the audio apparatus 14, may be placed anywhere remotefrom the audio apparatus 14. Therefore, since, for example, themicrophone unit 45 and the audio apparatus 14 may be placed on differentplacing surfaces, or placed even in different rooms, more free usingmodes of the audio system are available and versatility thereof may beimproved. Note that the numbers of the microphone 45 and the audioapparatus 14 are not limited to one but may be more than one.

Sixth Embodiment

FIGS. 21A and 21B are an elevation view and a side view, respectively,those illustrating a schematic structure of an image display apparatusaccording to a sixth embodiment. The image display apparatus accordingto the present embodiment is a TV 210 of what is called a stand typethat includes a housing 220, a display unit 230, a speaker 240, asupport member 250, a piezoelectric vibration unit 260, a detection unit270, and a microphone 281. The TV 210 applies a load to thepiezoelectric vibration unit 260. The housing 220 has a substantiallyrectangular external shape. The display unit 230 is retained in thehousing 220. The TV 210 is placed on a placing surface 290 of a desk orthe like that is horizontal. The desk is an example of the contactobject, and the placing surface 290 is an example of the contact surface(the placing surface) with which the TV 210 is in contact.

As illustrated in FIG. 21B, the TV 210 in normal use is supported on theplacing surface 290 by the support member 250 provided on a rear sidefor supporting the piezoelectric vibration unit 260 and the housing 220.The support member 250 is preferably provided in such a manner that aninclination angle thereof is adjustable with respect to the housing 220.

The display unit 230 is a thin display device such as, for example, aliquid crystal display, a plasma display, an organic EL display, or aninorganic EL display. The speaker 240 is, for example, a sound outputdevice such as the dynamic speaker or a capacitor speaker.

The detection unit 270 detects whether the piezoelectric vibration unit260 is in contact with the placing surface 290, that is, detects acontact state between the placing surface (the contact surface) 290 andthe piezoelectric vibration unit 260. The detection unit 270, similarlyto the detection unit 90 according to the fourth embodiment, isconstituted by using the device capable of detecting the contact statebetween the piezoelectric vibration unit 260 the placing surface 290such as, for example, the infrared sensor, the ultrasonic sensor, theproximity sensor, the mechanical switch, the camera, the pressuresensor, or the like. The detection unit 270 may be constituted by usingthe piezoelectric vibration unit 260 by using an output thereof as thesensor.

The microphone 281, together with a memory unit described later,constitutes a recording unit for recording the frequency characteristicsof the sound generated from the contact surface (the placing surface290) of the desk or the like in contact with the piezoelectric vibrationunit 260. The recording unit obtains the sound generated from thecontact surface by using the microphone 281 and stores the sound in thememory unit. The memory unit is arranged in the housing 220.

FIG. 22 is a schematic perspective view of a section illustrated in anexploded view of a front side of the housing 220 of FIG. 21A. Thehousing 220 includes a front bezel 221 and a rear cover 223 thoseretaining, therebetween, a display panel module 222 constituting thedisplay unit 230. The front bezel 221 is an exterior cover on a frontside of the TV 210. The display panel module 222 is exposed to the frontside through an opening of the front bezel 221. The display panel module222, when, for example, the display unit 230 is the liquid crystaldisplay, includes a liquid crystal panel and a backlight unit. A rearside of the display panel module 222 is formed with a flat plate-shapedpanel chassis made of a metal such as aluminum or iron. The panelchassis is provided with, on a rear side thereof, for example, anelectric circuit board for displaying an image such as a control board,a drive board, a TV tuner substrate, and the like. The rear cover 223protects the electric circuit board mounted on the panel chassis of thedisplay panel module 222. The TV 210 according to the present embodimentis provided with a holder portion 300 for accommodating and retainingthe piezoelectric vibration unit 260 on a bottom side of the housing220. The piezoelectric vibration unit 260 is arranged at a portion ofthe housing opposite to the placing surface (the contact surface) 290.The holder portion 300 has a slit 301 with a uniform width extending,for example, in a direction substantially vertical to the TV 210 in useand opening to a bottom surface 220 a of the rear cover 223 of thehousing 220.

The piezoelectric vibration unit 260 includes a piezoelectric element261, an O-ring 262, and a cap 263 that serves as the insulating covermember, and has a configuration similar to the piezoelectric vibrationunit 60 according to the first embodiment. Therefore, in this embodimentalso, the piezoelectric element 261 is constituted by using thelaminated piezoelectric element of the stack type.

The laminated piezoelectric element 261, as illustrated in a partiallyenlarged cross-sectional view of FIG. 23, has one lateral end portionhaving the first lead connection portion and the second lead connectionportion those described in the first embodiment and fixed to the slit301 of the holder portion 300 of the housing 220 via adhesive 302 (forexample, epoxy resin). The other end portion of the laminatedpiezoelectric element 261 is capped with the cap 63 and fixed by theadhesive 302.

The cap 263 includes an entry portion 263 a and a protrusion portion 263b. When the cap 263 is attached to the laminated piezoelectric element261, the entry portion 263 a is positioned inside the slit 301, and theprotrusion portion 263 b protrudes from the housing 220. The O-ring 262is provided to a circumference of the entry portion 263 a positionedinside the slit 301. When the piezoelectric vibration unit 260 isattached to the holder portion 300 and the front bezel 221 is attachedto the housing 220, the protrusion portion 263 b of the cap 263protrudes from the bottom surface 220 a of the housing 220. Theprotrusion portion 263 b of the cap 263 has a facing surface 263 copposite to the bottom surface 220 a of the housing 220. As illustratedin FIG. 23, when the laminated piezoelectric element 261 has no voltageapplied thereto and thus is not extending and contracting, the facingsurface 263 c is spaced apart from the bottom surface 220 a by thedistance d.

FIG. 24 is a functional block diagram of a section of the TV 210according to the present embodiment. The TV 210 includes, in addition tothe display unit 230, the speaker 240, the detection unit 270, therecording unit 280, and the laminated piezoelectric element 261 thosedescribed above, a signal reception unit 310, a DSP 320, a controller330, and a storage unit 340. The display unit 230, the detection unit270, the signal reception unit 310, and the storage unit 340 areconnected to the controller 330. The recording unit 280, as describedabove, includes the microphone 281 and the memory unit 282. The memoryunit 282 is connected to the controller 330. The speaker 240 and thelaminated piezoelectric element 261 are connected to the controller 330via the DSP 320. The DSP 320 may be built in the controller 330. Thememory unit 282 and the storage unit 340 may be constituted by using onememory.

The signal reception unit 310 has a known structure and receives abroadcast signal such as a video signal and a sound signal that istransmitted in a wired or wireless manner and viewed on the TV 210. Thecontroller 330 is a processor for controlling overall operations of theTV 210. The control unit 330 is one control unit in this embodiment butnot limited to such a structure. For example, the controller 330 may beconstituted by using a plurality of controllers for serving differentfunctions. The controller 330, via the DSP 320, applies the sound signalto the laminated piezoelectric element 261 and the speaker 240. Thesound signal may be based on music data stored in an internal memory orincluded in the broadcast signal.

The controller 330, based on the contact state between the piezoelectricvibration unit 260 and the placing surface 290 detected by the detectionunit 270, controls the sound signals to be applied to the laminatedpiezoelectric element 261 and the speaker 240. For example, when thedetection unit 270 detects that the piezoelectric vibration unit 260 andthe placing surface 290 are in contact with each other, the controller330 applies the sound signal to both the laminated piezoelectric element261 and the speaker 240. In this case, the piezoelectric vibration unit260 and the speaker 240 are driven at the same time. On the other hand,when the detection unit 270 detects that the piezoelectric vibrationunit 260 and the placing surface 290 are not in contact with each other,the controller 330 applies the sound signal to the speaker 240 alonewithout applying the sound signal to the laminated piezoelectric element261.

FIG. 25 is a flowchart illustrating an operation of the controller 330for applying the sound signal to the laminated piezoelectric element 261and the speaker 240. First, the controller 330 checks whether there isthe sound signal to be applied (step S201). When there is no soundsignal to be applied (No at step S201), the controller 330 ends the flowwithout applying the sound signal to the laminated piezoelectric element261 and the speaker 240. When there is the sound signal to be applied(Yes at step S201), the controller 330 determines to apply the soundsignal to the speaker 240 (step S202). Next, the controller 330 checkswhether the detection unit 270 is detecting the contact between thepiezoelectric vibration unit 260 and the placing surface 290 (stepS203). When the detection unit 270 is not detecting the contact betweenthe piezoelectric vibration unit 260 and the placing surface 290 (No atstep S203), the controller 330 applies the sound signal to the speaker240 alone without applying the sound signal to the laminatedpiezoelectric element 261 (step S207). In this case, the sound isgenerated not from the placing surface 290 but from the speaker 240alone.

On the other hand, when the detection unit 270 is detecting the contactbetween the piezoelectric vibration unit 260 and the placing surface 290(Yes at step S203), the controller 330 determines to apply the soundsignal to the laminated piezoelectric element 261 (step S204). Then, thecontroller 330 retrieves information about the frequency characteristicsof the sound (step S205). The information about the frequencycharacteristics of the sound is, for example, information about thefrequency characteristics of the sound generated from the speaker 240stored in the storage unit 340. The controller 330, based on theinformation thus retrieved, controls the sound signals to be applied to,for example, the laminated piezoelectric element 261 (step S206) andapplies the sound signal to the laminated piezoelectric element 261 andthe speaker 240 (step S207). The control of the sound signal carried outby the controller 330 at step S206 will be described in detail later. Inthis way, the sound is generated from both the placing surface 290 andthe speaker 240. The controller 330, while the TV 210 is on, repeats theseries of operations in FIG. 25 and thereby, based on the contact statebetween the piezoelectric vibration unit 260 and the placing surface290, controls the sound signals to be applied to the speaker 240 and thelaminated piezoelectric element 261.

Next, the control of the sound signal carried out by the controller 330at step S206 will be described. The controller 330 controls the soundsignal based on the information about the frequency characteristics ofthe speaker 240 retrieved from the storage unit 340. A region 400 inFIG. 26A represents an example of the frequency characteristics of thespeaker 240 stored in the storage unit 340. As can be seen in FIG. 26A,similarly to a typical tendency of the conventional dynamic speaker, thespeaker 240 has the frequency characteristic in which the sound pressureis low in a low frequency band. Therefore, when the sound is generatedby using the speaker 240 alone, it is difficult for a user watching theTV 210 to hear a low-pitched sound. Especially in a frequency band at afrequency f1 or lower, the sound pressure is 0, and the speaker 240cannot generate the sound at the frequency f1 or lower. Also, thespeaker 240 has the frequency characteristics that form a convex curvewith an apex around a frequency f3 (>f1). That is, when the speaker 240alone is used to generate the sound, the generated sound around thefrequency f3 is loud and, as the frequency becomes higher or lower thanthe frequency f3, a volume of the generated sound becomes smaller.

The controller 330, at step S206, controls the sound signal to beapplied to the piezoelectric element 261 in a manner compensating forthe lack of the sound pressure of the frequency characteristic of thespeaker 240. The compensation for the lack of the sound pressure of thefrequency characteristics includes, for example: increasing the soundpressure in a frequency band with a low sound pressure such that thesound in the frequency band is easily heard; increasing the soundpressure in the entire frequency band so as to increase the entirevolume; and increasing the sound pressure in a specific frequency bandso as to emphasize the sound in the specific frequency band. Thecontroller 330, for example, by compensating for the lack of the soundpressure in such a manner that the frequency characteristics similar tothat in the region 410 in FIG. 26A is exhibited, controls the soundsignal to be applied to the piezoelectric element 261. The controller330 applies the sound signal thus controlled to the piezoelectricelement 261 at step S207. The control of the sound signal in this mannerincreases the sound pressure in the low frequency band. Also, in afrequency band from the frequency f2 (f1<f2<f3) to a frequency f4 (>f3),the sound pressure becomes substantially even, reducing a difference inintensity of the sound at each frequency generated from the TV 210.

The controller 330, at step S205, may retrieve the information about thefrequency characteristics of the sound generated from the contactsurface recorded by the recording unit 280 and, at step S206, controlthe sound signal to be applied to the speaker 240 based on theinformation thus retrieved. In this case, after the TV 210 is placed onthe placing surface 290 and prior to actual use thereof, the controller330 applies a pure tone sweep signal at a uniform level as the soundsignal to the piezoelectric element 261 and vibrates the piezoelectricelement 261, thereby generating the sound from the contact surface. Thefrequency characteristics of the generated sound is acquired by themicrophone 281 of the recording unit 280 and recorded by the memory unit282. Then, during the actual use, the controller 330 retrieves theinformation about the frequency characteristics stored and, based onthis information, controls the sound signal to be applied to the speaker240. For the image display apparatus such as the TV 210 according to thepresent embodiment that is unlikely to be moved onto another placingsurface after being placed on the placing surface 290, after thefrequency characteristics is recorded by the memory unit 282, thecontroller 330 may repeatingly retrieve the recorded frequencycharacteristics. On the other hand, for the image display apparatus suchas a digital photo frame that is likely to be often moved onto otherplacing surfaces, every time the application of the sound signal to thepiezoelectric element 261 is determined at step S204, the frequencycharacteristics may be obtained from the microphone 281 and recorded bythe memory unit 282. In this case, the controller 330 retrieves thefrequency characteristics that has been recorded by the memory unit 282last time and, based on the retrieved information about the frequencycharacteristic, controls the sound signal to be applied to the speaker240.

A range 420 in FIG. 26B represents an example of the frequencycharacteristics of the sound generated from the contact surface recordedby the recording unit 280. Referring to the recorded frequencycharacteristics, the controller 330 controls the sound signal to beapplied to the speaker 240 in a manner compensating for the lack of thesound pressure, such that the frequency characteristics represented by arange 430 in FIG. 26B may be obtained. The controller 330 applies thesound signal thus controlled to the speaker 240 at step S207. Thecontroller 330, in order to obtain a sound pressure of desired frequencycharacteristics, may control both the sound signal to be applied to thepiezoelectric element 261 and the sound signal to be applied to thespeaker 240.

The DSP 320, on the digital signal from the controller 330, carries outnecessary signal processing such as equalizing processing, D/Aconversion processing, boosting processing, filtering process and thelike, and applies necessary sound signals to the speaker 240 and thepiezoelectric element 261.

A maximum voltage of a reproduced sound signal applied to the laminatedpiezoelectric element 261 may be, for example, in the range of 10 Vpp to50 Vpp but not limited thereto. The maximum voltage of the reproducedsound signal may be appropriately adjusted according to the weight ofthe TV 210 and functions of the speaker 240 and the laminatedpiezoelectric element 261. The sound signal applied to the laminatedpiezoelectric element 261 may have a biased DC voltage having themaximum voltage set therearound.

Not only the laminated piezoelectric element 261 but the piezoelectricelements generally have more power loss in proportion to the frequency.Therefore, the filtering process of the sound signal applied to thelaminated piezoelectric element 261 carried out by the DSP 320 is set tohave frequency characteristics to attenuate or cut at least a portion ofa frequency component of approximately 10 kHz to 50 kHz or higher, orfrequency characteristics to increase an attenuation ratio gradually orin stages. For example, the laminated piezoelectric element 281 has thefrequency characteristics having the cut-off frequency at approximately20 kHz similar to FIG. 8. The attenuation or cutting the high frequencycomponent in this manner allows reduction in power consumption as wellas suppression of heat generation by the laminated piezoelectric element261.

Next, with reference to FIG. 27, the arrangements of the piezoelectricvibration unit 260 and the support member 250 will be described. FIG. 27illustrates a state in which the TV 210 is in use and placed on theplacing surface 290 of the desk or the like that is horizontal. Asillustrated in FIG. 27, the TV 210 is supported on the placing surface290 by the piezoelectric vibration unit 260 and the support member 250.The point G represents a center of gravity of the TV 210. In FIG. 27,the support member 250 includes a lowermost portion 2501. The lowermostportion 2501 is a portion of the support member 250 that contacts theplacing surface 290 when the housing 220 is placed with the bottomsurface 220 a facing down on the placing surface 290 of the desk or thelike that is horizontal.

The piezoelectric vibration unit 260 includes a lowermost portion 2601.The lowermost portion 2601 is a portion of the piezoelectric vibrationunit 260 that contacts the placing surface 290 when the housing 220 isplaced with the bottom surface 220 a facing down on the placing surface290 of the desk or the like that is horizontal. The lowermost portion2601 is, for example, a tip of the cap 263.

The TV 210 includes a lowermost portion 2104. The lowermost portion 2104is a portion that contacts the placing surface 290 when the TV 210 isplaced with the bottom surface 220 a facing down on the placing surface290 of the desk or the like that is horizontal, assuming that there isno piezoelectric vibration unit 260. The lowermost portion 2104 of theTV 210 is, for example, an edge of the housing 220 but not limitedthereto. When the bottom surface 220 a is provided with a protrusionportion protruding therefrom, the protrusion portion may serve as thelowermost portion 2104 of the TV 210.

In FIG. 27, a dotted line L1 represents a line (a virtual line) passingthrough the center of gravity G of the TV 210 and perpendicular to theplacing surface 290 when the TV 210 is placed with the bottom surface220 a facing down on the placing surface 290 of the desk or the likethat is horizontal. A dashed line I is a line (a virtual line)connecting between the lowermost portion 2501 of the support member 250and the lowermost portion 2104 of the TV 210, assuming that there is nopiezoelectric vibration unit 260.

In FIG. 27, a region R1 is one of regions of the TV 210 separated by theline L1, and a region R2 is the other. The support member 250 isprovided in the region R1 and contacts the placing surface 290. Thebottom surface 220 a of the housing 220 having the piezoelectricvibration unit 260 is positioned in the region R2.

Preferably, the piezoelectric vibration unit 260 is positioned as closeto the dotted line L1 as possible within the region R2. The housing 220having the piezoelectric vibration unit 260 is preferably supported asclose to be vertical to the placing surface 290 as possible. Thereby,the load applied to the piezoelectric vibration unit 260 becomes heavierthan that when the piezoelectric vibration unit 260 is positioned remotefrom the line L1 within the region R2.

Preferably, the support member 250, within the range R1, is positionedas remote from the dotted line L1 as possible. Thereby, when thepiezoelectric vibration unit 260 is positioned as close to the dottedline L1 as possible, a sufficient distance may be ensured between thesupport member 250 and the piezoelectric vibration unit 260, allowingstable placement of the TV 210 on the placing surface 290.

Preferably, the lowermost portion 2601 of the piezoelectric vibrationunit 260, when the laminated piezoelectric element 261 extends maximumfrom the non-extending/contracting state thereof with no voltage appliedthereto, or at the time of maximum amplitude of the laminatedpiezoelectric element 261, is positioned between the dashed line I andthe placing surface 290. That is, the lowermost portion 2601, when thelaminated piezoelectric element 261 extends maximum from thenon-extending/contracting state thereof with no voltage applied thereto,or at the time of maximum amplitude of the laminated piezoelectricelement 261, preferably protrudes from the dashed line I toward theplacing surface 290. Thereby, the piezoelectric vibration unit 260 mayappropriately vibrate the placing surface 290.

Preferably, the lowermost portion 2601 of the piezoelectric vibrationunit 260, when the laminated piezoelectric element 261 contracts maximumfrom the non-extending/contracting state thereof with no voltage appliedthereto, or at the time of minimum amplitude of the laminatedpiezoelectric element 261, is positioned between the dashed line I andthe placing surface 290. That is, the lowermost portion 2601, when thelaminated piezoelectric element 261 contracts maximum from thenon-extending/contracting state thereof with no voltage applied thereto,or at the time of minimum amplitude of the laminated piezoelectricelement 261, preferably protrudes from the dashed line I toward theplacing surface 290. Thereby, the lowermost portion 2104 of the TV 210becomes less likely to contact the placing surface 290 and, for example,depending on a type of coating of the housing 220, the coating becomesless likely to come off. Also, the abnormal noise is less likely to begenerated between the lowermost portion 2104 and the placing surface290.

FIGS. 28A, 28B, and 28C are schematic diagrams explaining an operationto generate the sound carried out by the TV 210 according to the presentembodiment. When the piezoelectric vibration unit 260 of the TV 210generates the sound from the placing surface 290, the TV 210, asillustrated in FIG. 28A, is placed with the bottom surface 220 a of thehousing 220 facing down in such a manner that the cap 263 of thepiezoelectric vibration unit 260 and the support member 250 contact theplacing surface (the contact surface) 290 of the desk or the like.Thereby, the weight of the TV 210 is applied as the load to thepiezoelectric vibration unit 260. In a state illustrated in FIG. 28A,the laminated piezoelectric element 261 has no voltage applied theretoand thus is not extending and contracting.

In this state, when the laminated piezoelectric element 261 of thepiezoelectric vibration unit 260 is driven upon the reproduction soundsignal, the laminated piezoelectric element 261, as illustrated in FIGS.28B and 28C, uses a portion of the support member 250 in contact withthe placing surface (the contact surface) 290 as the support andvibrates extending and contracting according to the reproduction soundsignal, during which the cap 263 stays in contact with the placingsurface (the contact surface) 290. A difference between a length of thelaminated piezoelectric element 261 at the time of maximum extension anda length thereof at the time of maximum contraction is, for example,0.05 μm to 50 μm. Thereby, the extending and contracting vibration ofthe laminated piezoelectric element 261 is delivered to the placingsurface 290 via the cap 263, and thus the placing surface 290 vibratesand generates a sound serving as a vibration speaker. When thedifference between the length of the laminated piezoelectric element 261at maximum extend and the length thereof at maximum contraction issmaller than 0.05 μm, the placing surface 290 may possibly not bevibrated appropriately. On the other hand, when the difference isgreater than 50 μm, the placing surface 290 vibrates too much, possiblyrattling the TV 210.

As described above, the tip of the cap 263, at the time of maximumextension of the laminated piezoelectric element 261, preferablypositions between a line (the dotted line I in FIG. 27) connecting thelowermost portion 2501 of the support member 250 and the lowermostportion 2104 of the TV 210, assuming that there is no piezoelectricvibration unit 260. Also, the tip of the cap 263, at the time of maximumcontraction of the laminated piezoelectric element 261, preferablypositions between the virtual line and the placing surface 290.

Also preferably, the distance d between the bottom surface 220 a and thefacing surface 263 c of the cap 263 illustrated in FIG. 23 is longerthan a displacement amount of the laminated piezoelectric element 261from the non-extending/contracting state thereof with no voltage appliedthereto to the maximum contraction state. Thereby, when the laminatedpiezoelectric element 261 contracts maximum (a state illustrated in FIG.28C), the bottom surface 220 a of the housing 220 and the cap 263becomes less likely to come into contact with each other. As a result,the cap 263 becomes less likely to come off the piezoelectric element261.

A position of the piezoelectric element 260 on the bottom surface 220 a,a length of the laminated piezoelectric element 261 in the laminationdirection, a size of the cap 263 and the like are appropriatelydetermined in a manner satisfying the above conditions.

According to the image display apparatus of the present embodiment,since the piezoelectric element is used as the vibration source and thesound is generated from the placing surface (the contact surface) 290,the image display apparatus may generate the sound with better frequencycharacteristics than that of the sound generated by the conventionalimage display apparatus with similar cubic volume and weight thatgenerates the sound from the dynamic speaker alone. Also, since thepiezoelectric element enables reproduction of the sound in the lowfrequency band in which excellent frequency characteristics may behardly obtained with a small dynamic speaker, there is no need toprovide a large dynamic speaker to the image display apparatus, allowingreduction in size and weight of the image display apparatus. Especiallywhen excellent frequency characteristics may be obtained with thepiezoelectric element alone, there is no need to provide a speaker,allowing significant reduction in the size and the weight of the imagedisplay apparatus. Further, since the image display apparatus of thepresent embodiment generates the sound from the placing surface (thecontact surface) 290, the sound diffusivity is higher than that of theconventional image display apparatus that generates the sound from thedynamic speaker alone. Therefore, the conventional image displayapparatus has difficulty in delivering the sound to a user positionedelsewhere than in front of the speaker in comparison to the userpositioned in front of the speaker. However, the image display apparatusaccording to the present embodiment may deliver a homogeneous soundregardless of the position of the user.

Also, the image display apparatus according to the present embodimentemploys the laminated piezoelectric element 261 of the stack type as thepiezoelectric element, causes the laminated piezoelectric element 261 tovibrate extending and contracting in the lamination direction upon thereproduced sound signal, and delivers the extending and contractingvibration to the placing surface (the contact surface) 290. Therefore,excellent vibration transmission efficiency in the extension contractiondirection (a deformation direction) to the placing surface (the contactsurface) 290 may be obtained, and the placing surface (the contactsurface) 290 may be efficiently vibrated. Further, since the laminatedpiezoelectric element 261 contacts the placing surface (the contactsurface) 290 via the cap 263, the laminated piezoelectric element 261may be prevented from being damaged. Also, when the TV 210 is in use andthe cap 263 of the piezoelectric vibration unit 260 contacts the placingsurface (the contact surface) 290, since the weight of the TV 210 isapplied as the load to the cap 263, the cap 263 may reliably contactsthe placing surface (the contact surface) 290 and efficiently deliverthe extending and contracting vibration of the piezoelectric vibrationunit 260 to the placing surface (the contact surface) 290.

Also, since the image display apparatus according to the presentembodiment may directly deliver the vibration of, mainly, the laminatedpiezoelectric element to the placing surface (the contact surface),unlike conventional techniques those deliver the vibration of thelaminated piezoelectric element to another elastic body, soundgeneration does not depend on a maximum frequency at which the anotherelastic body may vibrate. Note that the maximum frequency at which theanother elastic body may vibrate is a reciprocal of the shortest timefrom deformation of the another elastic body caused by the piezoelectricelement to a restored state of the another elastic body allowing nextdeformation thereof. In view of this, the image display apparatusaccording to the present embodiment preferably has rigidity (flexuralstrength) to a degree not to be deformed in a curving manner by thedeformation of the piezoelectric element.

Seventh Embodiment

FIGS. 29A and 29B are an elevation view and a side view, respectively,those illustrating a schematic structure of an image display apparatusaccording to a seventh embodiment. The image display apparatus accordingto the present embodiment is the TV 210 of what is called the standtype. The following is a description of aspects of this TV 210 differentfrom that of the sixth embodiment, omitting aspects the same as those ofthe TV 210 of the sixth embodiment.

As illustrated in FIG. 29, the housing 220 includes the support member250 on a rear side thereof via a movable unit 250. An inclination angleof the housing 220 may be adjusted with the movable unit 251. Thesupport member 250 includes a flat plate-like member 252 which contactsthe placing surface (the contact surface) 290 and a columnar member 253for supporting the housing 220. The flat plate-like member 252 mayinclude an elastic member 254 on a bottom surface 252 a. The elasticmember 254 is made of, for example, rubber, silicone, polyurethanes, orthe like.

The TV 210 according to the present embodiment includes a holder portion300 for accommodating and retaining the piezoelectric vibration unit 260on the bottom surface 252 a of the flat plate-like member 252. Theholder portion 300 has a slit 301 with an even width extendingsubstantially perpendicular to the bottom surface 252 a and opening tothe bottom surface 252 a. In order to apply a sufficient load to thepiezoelectric vibration unit 260, the piezoelectric vibration unit 260,on the bottom surface 252 a, is preferably placed close to a linepassing through the center of gravity of the TV 210 and perpendicular tothe placing surface 290. For example, the piezoelectric vibration unit260 is preferably placed on the line passing through the center ofgravity of the TV 210 and perpendicular to the placing surface 290.

The elastic member 254, when the flat plate-like member 252 is placedwith the bottom surface 252 a facing down on the placing surface 290 ofthe desk or the like that is horizontal, receives the weight of the TV210 including the movable unit 251 and the support member 250 and iselastically deformed. That is, the elastic member 254 contracts in adirection perpendicular to the placing surface 290 due to the weight ofthe TV 210. An elastic deformation amount of the elastic member 254 whenthe laminated piezoelectric element 261 is not extending and contractinghaving no voltage applied thereto is preferably greater than adisplacement amount of the laminated piezoelectric element from theno-extending/contracting state thereof with no voltage applied theretoto the maximum extension state. Thereby, at the time of maximumextension of the laminated piezoelectric element 261, the elastic member254 is less likely to separate from the placing surface 290, allowing astable placement of the TV 210 on the placing surface 290.

Eighth Embodiment

FIG. 30 is a side view illustrating a schematic structure of an imagedisplay apparatus according to an eighth embodiment. The image displayapparatus according to the present embodiment is a TV 210 of what iscalled a wall-mount type. The following is a description of aspects ofthis TV 210 different from that of the sixth embodiment, omittingaspects the same as those of the TV 210 of the sixth embodiment.

The TV 210 illustrated in FIG. 30 includes a groove 224 for hookengagement in an upper area of a rear surface 220 b of the housing 220and, when the groove 224 is hung on a hook 255 attached to a wallsurface 291, held on the wall surface 291. The rear surface 220 b of thehousing 220 also includes the holder portion 300 for accommodating andretaining the piezoelectric vibration unit 260. The holder portion 300includes the slit 301 with an even width extending along a thicknessdirection of the TV 210 and opening to the rear surface 220 b.

In order to deliver the vibration of the piezoelectric vibration unit260 to the wall surface (the contact surface) 291 and generate the soundfrom the wall surface (the contact surface) 291, the TV 210 needs toapply the load to the piezoelectric vibration unit 260. FIG. 31 is aside view illustrating a state of the TV 210 assuming that there is nowall surface (contact surface) 291. FIG. 31 illustrates a state inwhich, although the TV 210 is supposed to be held at the groove 224 bythe hook 255, there is no wall surface (contact surface) 291 and thusthe piezoelectric vibration unit 260 is not supported on the wallsurface 291 by the cap 263. In FIG. 31, therefore, the TV 210 is held bythe hook 255 alone. An angle between a vertical line L2 and the rearsurface 220 b of the housing 220 formed when there is the wall surface(contact surface) 291 (as illustrated in FIG. 30) is represented by θ,and an angle between a vertical line L3 and the rear surface 220 b ofthe housing 220 formed when assuming that there is no wall surface(contact surface) 291 (as illustrated in FIG. 31) is represented by θ′.In order to apply the load to the piezoelectric vibration unit 260 whenthe TV 210 is in use, at least the θ′ needs to be greater than the θ.Also, in order to apply a heavier load to the piezoelectric vibrationunit 260, the θ′ is preferably a wider angle. A position of thepiezoelectric element 260 on the rear surface 220 b, the length of thelaminated piezoelectric element 261 in the lamination direction, thesize of the cap 263, the center of gravity of the TV 210, an attachingposition and a shape of the hook 255 and the like are appropriatelydetermined in a manner satisfying the above conditions.

Ninth Embodiment

FIGS. 32A, 32B, and 32C are an external perspective view, an elevationview, and a side view, respectively, those illustrating a schematicstructure of an image projection apparatus according to a ninthembodiment. The image projection apparatus according to the presentembodiment is a projector 510 of what is called a stand type andincludes a housing 520, a projection unit 530, a speaker 540, apiezoelectric vibration unit 560, a detection unit 570, and a microphone581. The projector 510, for use, is placed on a placing surface 590 thatis horizontal such as the desk. At this time, the projector 510 issupported by the piezoelectric vibration unit 560 and a rear bottomportion 520 b of the housing 520 and applies a load to the piezoelectricvibration unit 560. The projector 510, on a rear surface thereof,includes various signal input terminals such as a USB terminal forconnecting to a personal computer, a video terminal for signal input, aVGA (Video Graphic Array) terminal, and the like. The housing 520 has anexternal shape of substantial rectangular parallelepiped. The projectionunit 530 is retained on the housing 520. The desk is an example of thecontact object, and the placing surface 590 is an example of the contactsurface (the placing surface 590) in contact with the projector 510.

The projection unit 530 is a projection lens for displaying a magnifiedimage of an image display element on a projection plane such as a screenand the like. The speaker 540 is a sound output device such as, forexample, the dynamic speaker, the capacitor speaker, and the like.

The detection unit 570 detects whether the piezoelectric vibration unit560 is in contact with the placing surface 590, that is, a contact statebetween the placing surface (the contact surface) 590 and thepiezoelectric vibration unit 560. The detection unit 570, similarly tothe detection unit 90 of the fourth embodiment, is constituted by usingthe device capable of detecting the contact state between thepiezoelectric vibration unit 560 and the placing surface 590 such as,for example, the infrared sensor, the ultrasonic sensor, the proximitysensor, the mechanical switch, the camera, the pressure sensor, or thelike. The detection unit 570 may be constituted by using thepiezoelectric vibration unit 560 by using an output thereof as thesensor.

The microphone 581, together with a memory unit described later,constitutes a recording unit for recording the frequency characteristicsof the sound generated from the contact surface (the placing surface590) of the desk in contact with the piezoelectric vibration unit 560.The recording unit obtains the sound generated from the contact surfaceby using the microphone 581 and stores the sound in the memory unit. Thememory unit is arranged in the housing 520.

FIG. 33 is a schematic perspective view of a section illustrated in anexploded view of a bottom side of the housing 520 of FIG. 32. Thehousing 520 includes a body casing 521 and a bottom cover 522. The bodycasing 521 is an external cover of the projector 510 and contains, forexample, an image projection system 523, a cooling mechanism 524, anelectronic circuit board 525, a power supply unit 526, and the like. Theimage projection mechanism 523 includes a light source and the imagedisplay element. As the image display element, for example, the liquidcrystal is used when the projector 510 is of an LCD (Liquid-CrystalDisplay) type, or DMD (Digital Micromirror Device) is used when theprojector 510 is of a DLP (Digital Light Processing) type. The lightsource, when driven by the power supply unit 526, emits projection lightto the image display element and thus displays an image on the screenthrough the projection unit 530. The cooling mechanism 524 is, forexample, a cooling fan for cooling down the image projection mechanism523 and exhausts heat from an exhaust vent 527. The electronic circuitboard 525 controls each mechanism of the projector 510. The projector510 according to the present embodiment, on the bottom side of thehousing 520, includes a holder portion 600 for accommodating andretaining the piezoelectric vibration unit 560. The piezoelectricvibration unit 560 is arranged at a portion of the housing opposite tothe placing surface (the contact surface) 590. The holder portion 600has a slit 601 with an even width extending in a direction substantiallyperpendicular to the bottom cover 522 of the projector 510 and openingto the bottom cover of the housing 520. Also, the bottom cover 522includes a hole 522 a that allows the piezoelectric vibration unit 560to contact the placing surface (contact surface) 590.

The piezoelectric vibration unit 560 includes a piezoelectric element561, an O-ring 562, and a cap 563 that serves as the insulating covermember, and has a structure similar to the piezoelectric vibration unit60 described in the first embodiment. In the present embodiment also,the piezoelectric element 561 is constituted by using the laminatedpiezoelectric element of the stack type.

The laminated piezoelectric element 561, as illustrated in a partialenlarged cross-sectional view of FIG. 34, includes one lateral endportion having the first lead connection unit and the second leadconnection unit described in the first embodiment fixed to the slit 601of the support portion 600 of the housing 520 via adhesive 602 (forexample, the epoxy resin). The other end portion of the laminatedpiezoelectric element 561 is capped with a cap 563 and fixed by theadhesive 602.

The cap 563 includes an entry portion 563 a and a protrusion portion 563b. When the cap 563 is attached to the laminated piezoelectric element561, the entry portion 563 a is positioned inside the slit 601, and theprotrusion portion 563 b protrudes from the housing 520. The O-ring 562is provided to a circumference of the entry portion 563 a positionedinside the slit 601. When the piezoelectric vibration unit 560 isattached to the holder portion 600 and the bottom cover 522 is attachedto the housing 520, the protrusion portion 563 b of the cap 563protrudes from the bottom surface 520 a. The protrusion portion 563 b ofthe cap 563 has a facing surface 563 c opposite to a bottom surface 520a of the housing 520. As illustrated in FIG. 34, when the laminatedpiezoelectric element 561 has no voltage applied thereto and thus is notextending and contracting, the facing surface 563 c is spaced apart fromthe bottom surface 520 a by the distance d.

FIG. 35 is a functional block diagram of a section of the projector 510according to the present embodiment. The projector includes, in additionto the image projection mechanism 523, the projection unit 530, thespeaker 540, the detection unit 570, the recording unit 580, and thelaminated piezoelectric element 561 those described above, a signalinput unit 610, a DSP 620, a controller 630, and a storage unit 640. Theimage projection mechanism 523, the detection unit 570, the signal inputunit 610, and the storage unit 640 are connected to the controller 630.The storage unit 580 includes the microphone 581 and the memory unit 582as described above. The memory unit 582 is connected to the controller630. The projection unit 530 is connected to the controller 630 via theimage projection mechanism 523. The speaker 540 and the laminatedpiezoelectric element 561 are connected to the controller 630 via theDSP 620. The DSP 620 may be built in the controller 630. The memory unit582 and the storage unit 640 may be constituted by using one memory.

The signal input unit 610 has a known structure and, from various signalinput terminals, inputs a signal such as the video signal and the soundsignal to be viewed by using the projector 510. The controller 630 is aprocessor for controlling overall operations of the projector 510. Thecontroller 630 is structured as one control unit in this embodiment butnot limited to such a structure. For example, the controller 630 may beconstituted by using a plurality of controllers for serving differentfunctions. The controller 630, via the DSP 620, applies the soundsignals to the laminated piezoelectric element 661 and the speaker 640.The sound signal may be based on the music data stored in the internalmemory or included in the input signal.

The controller 630, based on the contact state between the piezoelectricvibration unit 560 and the placing surface 590 detected by the detectionunit 570, controls the sound signals to be applied to the laminatedpiezoelectric element 561 and the speaker 540. For example, when thedetection unit 570 detects that the piezoelectric vibration unit 560 andthe placing surface 590 are in contact with each other, the controller630 applies the sound signals to the laminated piezoelectric element 561and the speaker 540. In this case, the piezoelectric vibration unit 560and the speaker 540 are driven at the same time. On the other hand, whenthe detection unit 570 detects that the piezoelectric vibration unit 560and the placing surface 590 are not in contact with each other, thecontroller 630 applies the sound signal to the speaker 540 alone withoutapplying the sound signal to the laminated piezoelectric element 561.

FIG. 36 is a flowchart illustrating an operation of the controller 630for applying the sound signals to the laminated piezoelectric element561 and the speaker 540. First, the controller 630 checks whether thereis the sound signal to be applied (step S301). When there is no soundsignal to be applied (No at step S301), the controller 630 ends the flowwithout applying the sound signal to the laminated piezoelectric element561 and the speaker 540. When there is the sound signal to be applied(Yes at step S301), the controller 630 determines to apply the soundsignal to the speaker 540 (step S302). Next, the controller 630 checkswhether the detection unit 570 is detecting the contact between thepiezoelectric vibration unit 560 and the placing surface 590 (stepS303). When the detection unit 570 is not detecting the contact betweenthe piezoelectric vibration unit 560 and the placing surface 590 (No atstep S303), the controller 630 applies the sound signal to the speaker540 alone without applying the sound signal to the laminatedpiezoelectric element 561 (step S307). In this case, the sound isgenerated not from the placing surface 590 but from the speaker 540.

On the other hand, when the detection unit 570 is detecting the contactbetween the piezoelectric vibration unit 560 and the placing surface 590(Yes at step S303), the controller 630 determines to apply the soundsignal to the laminated piezoelectric element 561 (step S304). Then, thecontroller 630 retrieves information about the frequency characteristicsof the sound (step S305). The information about the frequencycharacteristics of the sound is, for example, information about thefrequency characteristics of the sound generated from the speaker 540stored in the storage unit 640. The controller 630, based on theinformation thus retrieved, controls the sound signal applied to, forexample, the laminated piezoelectric element 561 (step S306) and appliesthe sound signals to the laminated piezoelectric element 561 and thespeaker 540 (step S307). The control of the sound signal carried out bythe controller 630 at step S306 will be described in detail later. Inthis way, the sound is generated from both the placing surface 590 andthe speaker 540. The controller 630, while the projector 510 is on,repeats the series of operations in FIG. 36 and thereby, based on thecontact state between the piezoelectric vibration unit 560 and theplacing surface 590, controls the sound signals to be applied to thespeaker 540 and the laminated piezoelectric element 561.

Next, the control of the sound signal carried out by the controller 630at step S306 will be described. The controller 630 controls the soundsignal based on the information about the frequency characteristics ofthe speaker 540 retrieved from the storage unit 640. A region 700 inFIG. 37A represents an example of the frequency characteristics of thespeaker 540 stored in the storage unit 640. As can be seen in FIG. 37A,similarly to the typical tendency of the conventional dynamic speaker,the speaker 540 has the frequency characteristics in which the soundpressure is low in the low frequency band. Therefore, when the sound isgenerated by using the speaker 540 alone, it is difficult for the userviewing the image projected by the projector 510 to hear the low-pitchedsound. Especially in a frequency band at the frequency f1 or lower, thesound pressure is 0, and the speaker 240 is unable to generate the soundat the frequency f1 or lower. Also, the speaker 540 has the frequencycharacteristics that form the convex curve with the apex around thefrequency f3 (>f1). That is, when the speaker 540 alone generates thesound, the generated sound around the frequency f3 is loud and, as thefrequency becomes higher or lower than the frequency f3, the volume ofthe generated sound becomes smaller.

The controller 630, at step S306, controls the sound signal to beapplied to the piezoelectric element 561 in a manner compensating forthe lack of the sound pressure of the frequency characteristic of thespeaker 540. The compensation for the lack of the sound pressure of thefrequency characteristics includes, for example: increasing the soundpressure in a frequency band with a low sound pressure such that thesound in the frequency band is easily heard; increasing the soundpressure in the entire frequency band so as to increase the entirevolume; and increasing the sound pressure in a specific frequency bandso as to emphasize the sound in the specific frequency band. Thecontroller 630, for example, by compensating for the lack of the soundpressure so as to exhibit the frequency characteristics similar to theregion 710 in FIG. 37A, controls the sound signal to be applied to thepiezoelectric element 561. The controller 630 applies the sound signalthus controlled to the piezoelectric element 561 at step S307. Thecontrol of the sound signal in this manner increases the sound pressurein the low frequency band. Also, in the frequency band from thefrequency f2 (f1<f2<f3) to the frequency f4 (>f3), the sound pressurebecomes substantially even, reducing a difference in sound intensity ofeach frequency generated from the projector 510.

The controller 630, at step S305, may retrieve the information about thefrequency characteristics of the sound generated from the contactsurface recorded by the recording unit 580 and, at step S306, controlthe sound signal to be applied to the speaker 540 based on theinformation thus retrieved. In this case, after the projector 510 isplaced on the placing surface 590 and prior to actual use thereof, thecontroller 630 applies the pure tone sweep signal at an even level asthe sound signal to the piezoelectric element 561 and vibrates thepiezoelectric element 561, thereby generating the sound from the contactsurface. The frequency characteristics of the generated sound isacquired by the microphone 581 of the recording unit 580 and recorded inthe memory unit 582. Then, during actual use, the controller 630retrieves the information about the frequency characteristics recordedand controls the sound signal to be applied to the speaker 540 based onthis information.

A range 720 in FIG. 37B represents an example of the frequencycharacteristics of the sound generated from the contact surface recordedby the recording unit 580. Based on the recorded frequencycharacteristics, the controller 630 controls the sound signal to beapplied to the speaker 540 by, for example, compensating for the lack ofthe sound pressure, so as to be able to obtain the frequencycharacteristics represented by a range 730 in FIG. 37B. The controller630 applies the sound signal thus controlled to the speaker 540 at stepS307. The controller 330, in order to obtain a sound pressure of desiredfrequency characteristics, may control both the sound signal to beapplied to the piezoelectric element 561 and the sound signal to beapplied to the speaker 540.

The DSP 620, on the digital signal from the controller 630, carries outnecessary signal processing such as the equalizing processing, the D/Aconversion processing, the boosting processing, the filtering processand the like, and applies a necessary sound signal to the speaker 540and the piezoelectric element 561.

A maximum voltage of a reproduced sound signal applied to the laminatedpiezoelectric element 561 may be, for example, in the range of 10 Vpp to50 Vpp but not limited thereto. The maximum voltage of the reproducedsound signal may be appropriately adjusted according to the weight ofthe projector 510 and functions of the speaker 540 and the laminatedpiezoelectric element 561. The sound signal applied to the laminatedpiezoelectric element 561 may have the biased DC voltage having themaximum voltage set therearound.

The filtering process for the sound signal applied to the laminatedpiezoelectric element 561 carried out by the DSP 620 is set to have thefrequency characteristics to attenuate or cut at least a portion of thefrequency component of approximately 10 kHz to 50 kHz or higher, orfrequency characteristics to increase the attenuation ratio gradually orin stages. For example, the laminated piezoelectric element 561 has thefrequency characteristics having the cut-off frequency at approximately20 kHz similarly to FIG. 8. Attenuation or cutting the high frequencycomponent in this manner allows reduction in power consumption as wellas suppression of heat generation by the laminated piezoelectric element561.

Next, with reference to FIG. 38, the arrangement of the piezoelectricvibration unit 560 will be described. FIG. 38 illustrates a state inwhich the projector 510 is in use and placed on the placing surface 590of the desk or the like that is horizontal. As illustrated in FIG. 38,the projector 510 is supported on the placing surface 590 by thepiezoelectric vibration unit 560 and the rear bottom portion 520 b ofthe housing 520. A point G represents the center of gravity of theprojector 510. In FIG. 38, the piezoelectric vibration unit 560 includesa lowermost portion 5601. The lowermost portion 5601 is a portion of thepiezoelectric vibration unit 560 that contacts the placing surface 590when the housing 520 is placed with the bottom surface 520 a facing downon the placing surface 590 of the desk or the like that is horizontal.The lowermost portion 5601 is, for example, a tip of the cap 563.

In FIG. 38, the dotted line L1 is a line (a virtual line) that ispassing through the center of gravity G of the projector 510 andperpendicular to the placing surface 590 when the projector 510 isplaced with the bottom surface 520 a facing down on the placing surface590 of the desk or the like that is horizontal. A region R1 is a rearregion of the projector 510 when the dotted line L1 separates theprojector 510. A region R2 is a front region of the projector 510. Arear bottom portion 520 b, within the region R1, contacts the placingsurface 590. The piezoelectric vibration unit 560 is provided on thebottom surface 520 a in the region R2.

Preferably, the piezoelectric vibration unit 560 is provided at aposition within a predetermined distance from the dotted line L1 on thebottom surface 520 a in the region R2. More preferably, thepiezoelectric vibration unit 560 is provided as close to the dotted lineL1 as possible. Preferably, the predetermined distance is a distance (afirst distance) where the sound pressure decreases by 5% or less incomparison to the sound pressure of the sound generated from the placingsurface (the contact surface) 590 when the piezoelectric vibration unit560 is positioned on the dotted line L1. Thereby, the load applied tothe piezoelectric vibration unit 560 becomes greater than that when thepiezoelectric vibration unit 560 is provided at a position remote fromthe dotted line L1 on the bottom surface 520 a in the region R2. Thepredetermined distance may be a distance (a second distance) where thesound pressure decreases by 10% or less when the sound pressure is high,or a distance (a third distance) where the sound pressure decreases by20% or less when the sound pressure is sufficiently high.

Preferably, the rear bottom portion 520 b is positioned as remote fromthe dotted line L as possible in the region RE That is, the gravity Gpreferably positions more forwardly in the projector 10. In this way,when the piezoelectric vibration unit 560 is positioned as close to thedotted line L1 as possible, a sufficient distance may be ensured betweenthe rear bottom portion 520 b and the piezoelectric vibration unit 560.Accordingly, the projector 510 may be stably placed on the placingsurface 590, allowing the display of the projected image in a morestable manner.

FIGS. 39A, 39B, and 39C are schematic diagrams for explaining anoperation of the projector 510 to generate the sound. In order for thepiezoelectric vibration unit 560 of the projector 510 to cause theplacing surface 590 to generate the sound, the projector 510, asillustrated in FIG. 39A, is placed in such a manner that the bottomsurface 520 a of the housing 520 faces down and the cap 563 of thepiezoelectric vibration unit 560 and the rear bottom portion 520 bcontact the placing surface (the contact surface) 590 of the desk or thelike. Thereby, the weight of the projector is applied as the load to thepiezoelectric vibration unit 560. In a state illustrated in FIG. 39A,the laminated piezoelectric element 561 has no voltage applied theretoand thus is not extending and contracting.

In this state, when the laminated piezoelectric element 561 of thepiezoelectric vibration unit 560 is driven upon the reproduction soundsignal, the laminated piezoelectric element 561, as illustrated in FIGS.39B and 39C, by using the rear bottom portion 520 b as the support,vibrates extending and contracting according to the reproduction soundsignal, during which the cap 563 stays in contact with the placingsurface (the contact surface) 590. A difference between a length of thelaminated piezoelectric element 561 at the time of maximum extension anda length thereof at the time of maximum contraction is, for example,0.05 μm to 50 μm. Thereby, the extending and contracting vibration ofthe laminated piezoelectric element 561 is delivered to the placingsurface 590 via the cap 563, and the placing surface 590 vibrates andgenerates a sound serving as the vibration speaker. When the differencebetween the length of the laminated piezoelectric element 561 at thetime of maximum extension and the length thereof at the time of maximumcontraction is smaller than 0.05 μm, the placing surface 590 maypossibly not be vibrated appropriately. On the other hand, when thedifference is greater than 50 μm, the placing surface 590 vibrates toomuch, possibly rattling the projector 510.

The distance d between the bottom surface 520 a and the facing surface563 c of the cap 563 illustrated in FIG. 34 is preferably longer than adisplacement amount of the laminated piezoelectric element 561 from theno-extending/contracting state thereof to the maximum contraction state.Thereby, at the time of maximum contraction of the laminatedpiezoelectric element 561 (a state illustrated in FIG. 39C), the bottomsurface 520 a of the housing 520 and the cap 563 are less likely tocontact each other. As a result, the cap 563 is less likely to come offthe piezoelectric element 561.

A position of the piezoelectric element 560 on the bottom surface 520 a,a length of the laminated piezoelectric element 561 in the laminationdirection, a size of the cap 563 and the like are appropriatelydetermined in a manner satisfying the above conditions.

According to the image projection apparatus of the present embodiment,since the piezoelectric element is used as the vibration source and thesound is generated from the placing surface (the contact surface) 590,the image projection apparatus may generate the sound with betterfrequency characteristics than that of the sound generated by theconventional image projection apparatus with similar cubic volume andweight that generates the sound from the dynamic speaker alone. Also,since the piezoelectric element enables reproduction of the sound in thelow frequency band in which excellent frequency characteristics may behardly obtained with a small dynamic speaker, there is no need toprovide a large dynamic speaker to the image projection apparatus,allowing the reduction in size and weight of the image projectionapparatus. Especially when excellent frequency characteristics may beobtained with the piezoelectric element alone, there is no need toprovide a speaker. Therefore, the image projection apparatus may besignificantly small and thin. Further, since the image projectionapparatus of the present embodiment generates the sound from the placingsurface (the contact surface) 590, the sound diffusivity becomes higherthan the conventional image projection apparatus that generates thesound from the dynamic speaker alone. Therefore, the conventional imageprojection apparatus has difficulty in delivering the sound to a userpositioned elsewhere than in front of the speaker in comparison to theuser positioned in front of the speaker. However, the image projectionapparatus according to the present embodiment may generate a homogeneoussound regardless of the position of the user.

Also, the image projection apparatus according to the present embodimentuses the laminated piezoelectric element 561 of the stack type as thepiezoelectric element, causes the laminated piezoelectric element 561 tovibrate extending and contracting in the lamination direction upon thereproduction sound signal, and delivers the extending and contractingvibration to the placing surface (the contact surface) 590. Therefore,excellent vibration transmission efficiency in the extending andcontraction direction (the deformation direction) to the placing surface(the contact surface) 590 may be obtained, and the placing surface (thecontact surface) 290 may be efficiently vibrated. Further, since thelaminated piezoelectric element 261 contacts the placing surface (thecontact surface) 290 via the cap 563, the laminated piezoelectricelement 561 may be prevented from being damaged. Also, in use of theprojector 510, when the cap 563 of the piezoelectric vibration unit 560contacts the placing surface (the contact surface) 590, since the weightof the projector 510 is applied as the load to the cap 563, the cap 563may reliably contacts the placing surface (the contact surface) 590,whereby the extending and contracting vibration of the piezoelectricvibration unit 560 may be efficiently delivered to the placing surface(the contact surface) 590.

Also, since the image projection apparatus according to the presentembodiment may directly deliver the vibration of, mainly, the laminatedpiezoelectric element to the placing surface (the contact surface),unlike the conventional techniques those deliver the vibration of thelaminated piezoelectric element to another elastic body, soundgeneration does not need to depend on a maximum frequency at which theanother elastic body may vibrate. Note that the maximum frequency atwhich the another elastic body may vibrate is the reciprocal of theshortest time from deformation of the another elastic body caused by thepiezoelectric element the restored state of the another elastic bodyallowing next deformation thereof. In view of this, the image projectionapparatus according to the present embodiment preferably has rigidity(flexural strength) to a degree not to be deformed in a curving mannerby the deformation of the piezoelectric element.

Tenth Embodiment

FIGS. 40A, 40B, and 40C are an external perspective view, an elevationview, and a side view, respectively, those illustrating a schematicstructure of an image projection apparatus according to a tenthembodiment. The image projection apparatus according to the presentembodiment is a projector 510 of what is called the stand type similarto the ninth embodiment. The following is a description of aspects ofthis projector 510 different from that of the ninth embodiment, omittingaspects the same as those of the projector 510 of the ninth embodiment.

As illustrated in FIG. 40, the housing 520 includes two front supportportions 550 on a front side having the projection plane positionedthereon, and two rear support portions 551 on a rear side opposite tothe front side. The front support portions 550 and the rear supportportions 551 contact the placing surface 590 and support the housing520. An inclination angle of the housing 520 is adjustable by adjustinga height of the front supports 550. The front support portion 550 andthe rear support portion 551 may be provided with an elastic member onbottoms thereof. The elastic member is made of, for example, rubber,silicone, polyurethanes, or the like. Although in the present embodimentthere are two front support portions 550 and two rear support portions551, the numbers of the front support portions and rear support portionsare not limited thereto; there may be one front support portion 550 andtwo rear support portions 551, or two front support portions 550 and onerear support portion 551.

The projector 510 according to the present embodiment, on the bottom ofthe rear support portion 551, includes the holder portion 600 foraccommodating and retaining the piezoelectric vibration unit 560. Thepiezoelectric vibration unit 560 may be provided to either one of, orboth of, the two rear support portions 551. The holder portion 600 has aslit 601 with an even width extending along a direction substantiallyperpendicular to the bottom surface and opening to the bottom surface.

The elastic member, when the projector 510 is placed with the bottomsurface 520 a facing down on the placing surface 590 of the desk or thelike that is horizontal, receives the weight of the projector 510 as theload and is elastically deformed. That is, the elastic member contractsin a direction perpendicular to the placing surface 590 due to theweight of the projector 510. An elastic deformation amount of theelastic member, when the laminated piezoelectric element 561 has novoltage applied thereto and thus is not extending and contracting, ispreferably greater than the displacement amount of the laminatedpiezoelectric element 561 from the no-extending/contracting statethereof with no voltage applied thereto to the maximum extension state.Thereby, at the time of maximum extension of the laminated piezoelectricelement 561, the elastic member is less likely to separate from theplacing surface 590, allowing a stable placement of the projector 510 onthe placing surface 590.

According to the present embodiment, the piezoelectric vibration unit560 may be arranged on the bottom of the front support portion 550 butis preferably arranged at the rear support portion 551 in order tosuppress the blurring of the projected image. Here, the reason whyarranging the piezoelectric vibration unit 60 at the rear supportportion 551 rather than at the front support portion 550 reduces theblurring of the projected image will be described with reference to FIG.41. In FIG. 41, S represents a position of the projection plane on whichthe image is displayed, F represents the position of the front supportportion 550, and B represents the position of the rear support portion551. The position F is located between the position S and the positionB. Vibration amplitude of the projector 510 caused by the vibration ofthe piezoelectric vibration unit 560 is represented by a. In FIG. 41, inorder to show the blurring of the projected image in the same direction,a direction of the vibration caused when the piezoelectric vibrationunit 560 is positioned at the front support portion 550 and a directionof the vibration caused when the piezoelectric vibration unit 560 ispositioned at the rear support portion 551 are indicated opposite toeach other. That is, FIG. 41 illustrates, with respect to a referenceposition 800 when the piezoelectric vibration unit 560 is not vibrating,upward displacement of the front support portion 550 by the amplitude afrom the reference position 800 due to extension of the piezoelectricelement 561 and downward displacement of the rear support portion 551 bythe amplitude a from the reference position 800 due to the contractionof the piezoelectric element 561. When the piezoelectric vibration unit560 is positioned at the front support portion 550, the projected imageis upwardly displaced by a height H by using the rear support portion551 as the support. On the other hand, when the piezoelectric vibrationunit 560 is positioned at the rear support portion 551, the projectedimage is upwardly displaced by a height h by using the front supportportion 550 as the support. As is apparent from FIG. 41, with the sameamplitude a of these support portions, the displacement H of theprojected image caused when the piezoelectric vibration unit 560 ispositioned at the front support portion 550 is greater than thedisplacement h caused when the piezoelectric vibration unit 560 ispositioned at the rear support portion 551. Therefore, the piezoelectricvibration unit 560 is preferably positioned at the rear support portion551 rather than at the front support portion 550, thereby the projectedimage less blurs and the image is easy to see.

Eleventh Embodiment

FIG. 42 is a side view illustrating a schematic structure of an imageprojection apparatus according to an eleventh embodiment. The imageprojection apparatus according to the present embodiment is theprojector 510 of what is called a wall-mount type. The following is adescription of aspects of this projector 510 different from that of theninth embodiment, omitting aspects the same as those of the projector510 of the ninth embodiment.

The projector 510 illustrated in FIG. 42 includes, on the housing 520, asupport portion 552 in an arm shape extending forwardly of the projector510. A distal end of the support portion 552 takes a hook shape and,when the distal end is attached to a wall surface 591 such as awhiteboard or the like, the projector 510 is held on the wall surface591. A contact area of the support portion 552 in contact with the wallsurface 591 includes the holder portion 600 for accommodating andretaining the piezoelectric vibration unit 560. The holder portion 600has the slit 601 with a uniform width extending extends a directionperpendicular to the wall surface 591 when the projector 510 is in useand opening to the contact area of the support portion 552 in contactwith the wall surface 591. Since the support portion 552 supports theprojector 510, the load of the projector 510 is applied to apiezoelectric element portion 560 via the support portion 552, and thesound is generated from the wall surface (the contact surface) 591. Inthis way, since the sound may be provided to the user viewing the wallsurface such as the whiteboard from the wall surface the user isviewing, the user may have a sense of presence similar to that obtainedfrom what is called a panel speaker that generates the sound from adisplay panel.

The disclosure herein is not limited to the above embodiments but may bevaried or modified in a number of manners. For example, in the first tofifth embodiments described above, the structure to fix thepiezoelectric vibration unit 60 to the holder portion 100 is not limitedto that illustrated in FIG. 5. The piezoelectric vibration unit 60 maybe retained by the holder portion 100 in manners as illustrated in FIGS.43A to 43C, for example. The holder portion 100 illustrated in FIG. 43Aincludes a wide slit 101 a opening to the bottom surface 20 b and anarrow slit 101 b contiguous to the slit 101 a. The laminatedpiezoelectric element 61 has one end positioned within the narrow slit101 b and a lateral side fixed to the slit 101 b via the adhesive 102. Agap between the wide slit 101 a and the laminated piezoelectric element61 is filled with a filler 103 such as silicone, gel or the like whichdoes not interfere with extension and contraction of the laminatedpiezoelectric element 61. When the piezoelectric vibration unit 60 isretained by the holder portion 100 in this manner, without the necessityto use a waterproof packing such as the O-ring, the audio apparatus 10may be more reliably waterproofed. Further, when a portion of thelaminated piezoelectric element 61 protruding from the bottom surface 20b is capped with an insulating cap, the laminated piezoelectric element61 may be reliably insulated.

The holder portion 100 illustrated in FIG. 43B includes a tapered slit101 c which becomes wider toward the bottom surface 20 b and a narrowslit 101 d contiguous to the tapered slit 101 c. The laminatedpiezoelectric element 61 has one end positioned within the narrow slit101 d and a lateral side fixed to the slit 101 d via the adhesive 102. Agap between the tapered slit 101 c and the laminated piezoelectricelement 61 is filled with the filler 103 such as silicone, gel or thelike which does not interfere with extension and contraction of thelaminated piezoelectric element 61. This configuration offers anadvantage to be able to obtain an effect similar to that of the holderportion 100 of FIG. 43A and, further, an advantage to facilitateattachment of the laminated piezoelectric element 61 to the holderportion 100.

The holder portion 100 illustrated in FIG. 43C includes the slit 101with a uniform width, and the laminated piezoelectric element 61 has oneend surface fixed to the slit 101 via the adhesive 102. The O-ring 62 isprovided to an appropriate position on the laminated piezoelectricelement 61 inside the slit 101. The laminated piezoelectric element 61retained in this manner is advantageous in terms of wiring a lead wireespecially when the laminated piezoelectric element 61 has the leadconnection portions formed on the side electrodes as illustrated in FIG.4.

Also, the piezoelectric element is not limited to the laminatedpiezoelectric element of the stacked type described above but may be aunimorph, a bimorph, or a multilayer bimorph element. FIG. 44 is adiagram illustrating a schematic structure of a section using thebimorph. A bimorph 65 has an elongated rectangular shape with onesurface 65 a exposed to the bottom surface 20 b of the housing 20 andboth longitudinal ends supported by the holder portion 100. The holderportion 100 includes an opening portion 101 e that supports the bimorph65 and has a curved internal surface facing a rear surface 65 b of thebimorph 65. With this structure, when the housing 20 is placed such thatthe bimorph 65 contacts the placing surface and the bimorph 65 is drivenupon the audio signal, the bimorph 65 vibrates in a bending (curving)manner. Thereby, the vibration of the bimorph 65 is delivered to theplacing surface (the contact surface), and the placing surface (thecontact surface) generates a reproduced sound functioning as thevibration speaker. Note that the surface 65 a of the bimorph 65 may havea coating layer made of polyurethane or the like formed thereon.

Further, in FIG. 7, an LPF having characteristics similar to the LPF 123may be provided between the signal processor circuit 121 and the boostercircuit 122. In FIG. 7, also, the equalizer or the like of the signalprocessor circuit 121 may have the function of the LPF 123 so as toallow omission of the LPF 123.

Further, although in the first to fifth embodiments described above thecontact object is the table and the contact surface is the placingsurface of the table that is horizontal, the contact surface is notlimited thereto.

Also, in the sixth embodiment, the piezoelectric vibration unit 260 maybe arranged on a surface where the support portion 250 contacts theplacing surface 290. That is, the piezoelectric vibration unit 260 maybe arranged at a portion of the support member 250 opposite to theplacing surface (the contact surface) 290. In the eighth embodiment,also, the TV 210, without using the hook 255, may be directly secured tothe wall surface (the contact surface) 291 by a screw or the like. Inthe sixth to eighth embodiments, also, the speaker 240, the detectingunit 270, the recording unit 280, and the storage unit 340 may beomitted as appropriate. In the sixth embodiment, further, depending onthe shape of the TV 210, i.e., when the housing 220 has, for example, abox-shape, the support member 250 may be omitted.

Further, although the image display apparatus is the TV 210 in the sixthto eighth embodiments described above, the image display apparatus isnot limited thereto. The disclosure herein may be implemented by anyimage display apparatus capable of displaying a still image or a videoimage and, simultaneously, generating the sound such as, for example,the personal computer, an LCD monitor, a digital photo frame, avideophone apparatus, and the like.

In ninth embodiment, for example, the piezoelectric vibration unit 560may be arranged in the region R1 in FIG. 38. That is, the piezoelectricvibration unit 560 is arranged behind the center of gravity G of theprojector 510. In this case, the projector 510 is supported by thepiezoelectric vibration unit 560 and the front bottom portion of thehousing 520. In the ninth to eleventh embodiments described above, also,the speaker 540, the detection unit 570, the recording unit 580, and thestorage unit 640 may be omitted as appropriate.

Also, although the image projection apparatus in the ninth to eleventhembodiments described above is the projector 510 having one projectionunit, the image projection apparatus is not limited thereto. Thedisclosure herein may be implemented by any image projection apparatuscapable of displaying the still image or the video image and,simultaneously, generating the sound such as, for example, a planetariumprojector or the like having a plurality of projection units.

Also, the modification examples illustrated in FIGS. 43A to 43C and FIG.44 are applicable also to the above sixth to eleventh embodiments.Further, in the above embodiments and in the modification examples ofFIGS. 43A to 43C, the cap of the piezoelectric vibration unit may beomitted such that the piezoelectric vibration unit, at the end surfacethereof, contacts the contact surface directly, or via a vibrationdelivering member made of an insulating member or the like.

Further, although in the sixth to eleventh embodiments described abovethe desk or the wall surface serve as the contact object, and theplacing surface of the desk or the like that is horizontal or thevertical wall serve as the contact surface, the disclosure herein is notlimited thereto. The contact surface does not need to be a horizontal orvertical surface. Another contact object may be, for example, apartition for separating a space.

1. An image projection apparatus comprising: a housing; a piezoelectricvibration unit having a piezoelectric element; a projection unit,retained in the housing, configured to display an image on a projectionscreen; and a controller configured to control the piezoelectricelement, wherein when the controller applies a sound signal to thepiezoelectric element while a load of the image projection apparatus isapplied to the piezoelectric vibration unit, the piezoelectric elementis deformed causing deformation of the piezoelectric vibration unit, thepiezoelectric vibration unit projecting outwardly from the housing andretracting inwardly into the housing, whereby a contact surface incontact with the image projection apparatus is vibrated and generates asound.
 2. The image projection apparatus according to claim 1, whereinthe piezoelectric vibration unit is provided at a position within apredetermined distance from a center of gravity of the image projectionapparatus and opposite to the contact surface.
 3. The image projectionapparatus according to claim 1, comprising a support member configuredto support the housing, wherein the piezoelectric vibration unit isprovided at a portion of the support member opposite to the contactsurface.
 4. The image projection apparatus according to claim 3,comprising a front support portion positioned on a front side from thecenter of gravity of the image projection apparatus where the projectionscreen is located and a rear support portion positioned on a rear sideopposite to the front side having the projection screen, wherein thepiezoelectric vibration unit is arranged at the rear support portion. 5.The image projection apparatus according to claim 1, comprising adetection unit configured to detect a contact state between the contactsurface and the piezoelectric vibration unit, wherein the controllercontrols the piezoelectric element based on the contact state.
 6. Theimage projection apparatus according to claim 1, comprising a speaker,wherein the controller drives the speaker and the piezoelectric elementat the same time.
 7. The image projection apparatus according to claim6, comprising a storage unit configured to store frequencycharacteristics of the speaker, wherein the controller controls thepiezoelectric element based on the frequency characteristics of thespeaker stored.
 8. The image projection apparatus according to claim 7,wherein the controller controls a sound signal to be applied to thepiezoelectric element in a manner compensating for the lack of the soundpressure of the frequency characteristics of the speaker stored.
 9. Theimage projection apparatus according to claim 6, comprising a recordingunit configured to record frequency characteristics of a sound generatedfrom the contact surface, wherein the controller controls the speakerbased on the frequency characteristics recorded.
 10. The imageprojection apparatus according to claim 9, wherein the control unitcontrols the sound pressure of the frequency characteristics of thespeaker in a manner compensating for the lack of the sound pressure ofthe frequency characteristics recorded.
 11. The image projectionapparatus according to claim 1, wherein the piezoelectric element is alaminated piezoelectric element and deformed extending and contractingalong a lamination direction.
 12. The image projection apparatusaccording to claim 1, wherein the piezoelectric vibration unit isprovided with a cover member configured to deliver the vibration causedby the deformation of the piezoelectric element to the contact surfaceand thereby vibrating the contact surface.
 13. The image projectionapparatus according to claim 1, wherein the contact surface is a placingsurface having the image projection apparatus placed thereon.
 14. Theimage projection apparatus according to claim 1, wherein the contactsurface is a wall surface having the image projection apparatus hungthereon.